• TABLE OF CONTENTS
HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 Abstract
 Introduction
 Literature review
 Estimation of genetic parameters...
 Influence of frame size and body...
 Genetic parameters and relationships...
 General conclusions
 Appendix A: Equations for a three-trait...
 Appendix B: Equations for a two-trait...
 References
 Biographical sketch














Title: Estimation of phenotypic and genetic relationships among hip height and productive and reproductive performance in Brahman cattle /
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Title: Estimation of phenotypic and genetic relationships among hip height and productive and reproductive performance in Brahman cattle /
Physical Description: xi, 136 leaves : ; 29 cm.
Language: English
Creator: Vargas Lucena, Carlos Alberto, 1949-
Publication Date: 2000
Copyright Date: 2000
 Subjects
Subject: Research   ( mesh )
Veterinary Medicine   ( mesh )
Cattle -- genetics   ( mesh )
Reproductive Behavior   ( mesh )
Sexual Behavior, Animal   ( mesh )
Department of Animal Science thesis, Ph. D   ( lcsh )
Dissertations, Academic -- College of Veterinary Medicine -- Department of Animal Science -- UF   ( lcsh )
Genre: bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )
 Notes
Summary: ABSTRACT: Covariance components for scrotal circumference at 18 mo of age (SC), age at puberty in heifers (AP), and hip height at 18 mo (HH18); effect of small (SFS; 120 cm), medium (MFS; 130 cm), and large (LFS; 140 cm) frame size of heifer on age at puberty, and on subsequent calving rate, calving date, survival rate, weaning rate, birth weight, preweaning ADG, weaning weight (WWT), and kilograms of calf per cow exposed for first- (P1D), second- (P2D) and third or greater-parity (P3D) dams; and relationships between weaning hip height (WHH), WWT, postweaning hip height growth (PHG), and HH18 were estimated in Brahman cattle. Covariances were estimated using REML fitting multi-trait animal models. Least-squares means estimated the effect of frame size on reproductive traits. Heritabilities for SC, AP, and HH18 were .28, .42, and .65. Genetic correlations between SC and AP; SC and HH18; and AP and HH18 were -.32, .19, and .25. Puberty occurred at younger ages in SFS and MFS than in LFS heifers. Calving rates in P2D and P3D were less among LFS than among SFS. Calf survival rate for P1D was less for LFS than for SFS and MFS. Weaning rates in P1D and P2D were less for LFS than for SFS and MFS. Weaning weights of calves from P1D and P3D were heavier for LFS than for SFS. Heritabilities for WHH-, WWT-, PHG-, and HH18-direct, and maternal averaged .69, .31, .13, .87; and .10, .18, .00, and .03, respectively. Negative genetic correlations existed between direct and maternal effects for WHH, WWT, PHG, and HH18. Selecting for increased SC favored earlier AP in heifers. Selecting for HH18 may not adversely affect SC but might have some detrimental effect on AP in female progeny.
Summary: ABSTRACT (cont.): Females of SFS and MFS surpassed LFS by demonstrating earlier calving dates, and greater calving, calf survival and weaning rates. There is a strong genetic relationship between WHH and WWT that has an impact on HH18. Thus, if the breeding objective is to manipulate growth to 18 mo of age, implementation of multiple trait breeding programs considering WHH and WWT will aid in the prediction of hip height at time of selection.
Summary: KEYWORDS: phenotypic parameters, genetic parameters, production, reproduction, Brahman, zebu, size, hip height, weight
Thesis: Thesis (Ph. D.)--University of Florida, 2000.
Bibliography: Includes bibliographical references (leaves 121-135).
Additional Physical Form: Also available on the World Wide Web; PDF reader required.
Statement of Responsibility: by Carlos A. Vargas L.
General Note: Printout.
General Note: Vita.
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Bibliographic ID: UF00100681
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 45837518
alephbibnum - 002566164
notis - AMT2445

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Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
    List of Tables
        Page viii
        Page ix
    Abstract
        Page x
        Page xi
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Literature review
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
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        Page 35
        Page 36
        Page 37
        Page 38
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        Page 40
        Page 41
    Estimation of genetic parameters for scrotal circumference, age at puberty in heifers, and hip height in Brahman cattle
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
    Influence of frame size and body condition on performance in Brahman cattle
        Page 56
        Page 57
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    Genetic parameters and relationships between hip height and weight in Brahman cattle
        Page 83
        Page 84
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        Page 103
        Page 104
    General conclusions
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
    Appendix A: Equations for a three-trait animal model
        Page 112
        Page 113
        Page 114
    Appendix B: Equations for a two-trait animal model with maternal effects
        Page 115
        Page 116
        Page 117
    References
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
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        Page 131
        Page 132
    Biographical sketch
        Page 133
Full Text











ESTIMATION OF PHENOTYPIC AND GENETIC RELATIONSHIPS AMONG HIP
HEIGHT AND PRODUCTIVE AND REPRODUCTIVE PERFORMANCE IN
BRAHMAN CATTLE
















By

CARLOS A. VARGAS L.


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA
2000































Copyright 2000

by

Carlos A. Vargas L.


































To Zuni, Carlos Alberto, and Ver6nica Josefina.















ACKNOWLEDGMENTS


The author wishes to express his sincere gratitude and appreciation to Drs. Timothy A.

Olson and Mauricio A. Elzo, chair and cochair of his supervisory committee, for their guidance,

constant encouragement, and insightful comments throughout his research and preparation of

this dissertation. The author would also like to thank the other members of the supervisory

committee Drs. Chad Chase, Jr., Ramon C. Littell, and Peter J. Chenoweth for their friendly

attitude and valuable advice throughout this study and in the preparation of this manuscript.

Special thanks is extended to the USDA-ARS-STARS at Brooksville, Florida, for

allowing the use of the Brahman data and to the Department of Animal Science of the

University of Florida for its support and assistance.

Gratitude is extended to his fellow graduate students (Rafael Roman, Javier Rosales,

Thais Diaz, and Andres Kowalski) and to Shirley Lugenbeel, for their cheerful support and

motivation.

Deepest gratitude and appreciation go to the author's parents, Pedro and Clementina,

and parents-in-law, Rodolfo and Graciela, for their encouragement and constant support

throughout the course of this task.















TABLE OF CONTENTS


page

ACKNOW LEDGM ENTS .............................................. iv

LIST O F TA B LE S ....................................... ........ . viii

A B ST R A C T ............................................... ........ x

CHAPTERS

1 IN TR OD U CTION .................................. . ..... 1

2 LITERATURE REVIEW .............................. ..... 6

Genetic Parameters for Hip Height, Scrotal Circumference,
and A ge at Puberty ............................ .......... 7
H eritabilities .................................. ..... 7
G enetic Correlations ............................ 12
Relationships Between Body Size and Performance in Females ....... 19
Reproductive Performance ............................ 21
Productive Performance .......................... 29
Relationships Between Hip Height and Weight ............... . 32
H ip H eight ........................................ 35
W meaning W eight ......................... ......... 36
Hip Height and Body Weight Relationships ............ . 39

3 ESTIMATION OF GENETIC PARAMETERS FOR SCROTAL
CIRCUMFERENCE, AGE AT PUBERTY IN HEIFERS, AND
HIP HEIGHT IN BRAHMAN CATTLE ...................... 42

Introduction ...................................... . 42
M materials and M ethods ............................... 43
Data Description and Animal Management .............. 43
Statistical A analysis .................................. 46












R results and D discussion ..................................... 48
H eritabilities ....................................... 48
G enetic Correlations ................................. 50
Im plications .................................. ......... 54
Su m m ary . . . . . . . . . . . . . . . . . . . . . .. . 55

4 INFLUENCE OF FRAME SIZE AND BODY CONDITION
ON PERFORMANCE IN BRAHMAN CATTLE ............... 56

Introduction ...................................... . 56
M materials and M ethods ............................... 57
Data Description and Animal Management .............. 57
Statistical A analysis .................................. 61
R results and D discussion ..................................... 63
Hip Height and Body Condition Score ................. 63
A ge at Puberty .......................... ......... 64
C alving R ate ............................ ......... 65
C alving D ate ....................................... 67
Survival R ate ........................... ......... 69
W meaning R ate ........................... ......... 70
B irth W eight ............................ ......... 72
W meaning W eight ................. .................. 74
Preweaning Average Daily Gain .................... . 76
Production Per Cow ................................. 77
Im plications .................................. ......... 80
Su m m ary . . . . . . . . . . . . . . . . . . . . . .. . 80

5 GENETIC PARAMETERS AND RELATIONSHIPS BETWEEN
HIP HEIGHT AND WEIGHT IN BRAHMAN CATTLE ......... 83

Introduction ...................................... . 83
M materials and M ethods ..................................... 84
D ata D description .................................... 84
Statistical A analysis .................................. 85
R results and D discussion ..................................... 88
Hip Height and Weight at Weaning . . . . . . . . 89
Hip Height at Weaning and Postweaning Hip Height Growth . 92
Weaning Weight and Hip Height at 18 Mo .............. 95
Breeding Values and Animal Rankings ..................99









Im plications .....................................
Su m m ary . . . . . . . . . . . . . . . . . . . .

6 GENERAL CONCLUSIONS ........................

APPENDIX A EQUATIONS FOR A THREE-TRAIT ANIMAL MODEL

APPENDIX B EQUATIONS FOR A TWO-TRAIT ANIMAL MODEL
WITH MATERNAL EFFECTS ............................

R E FE R E N C E S ..............................................

BIOGRAPHICAL SKETCH ....................................


. . ... 102
....... 102

. . ... 105

. . . . 112


. . . . 115

. . . . 118

. . ... 133















LIST OF TABLES


Table page

2- 1. Heritability estimates for hip height, scrotal circumference, and
age at puberty in heifers ........................................ 9

2-2. (Co)variance estimates for scrotal circumference and hip height ............ 13

2-3. Genetic and environmental correlations estimates for scrotal circumference,
age at puberty in heifers, hip height and yearling weight .............. 16

2-4. Heritability estimates for weaning weight in Brahman cattle and
Bos indicus crosses by geographical region ...................... 37

3-1. Additive genetic (co)variance estimates for scrotal circumference (SC),
age at puberty in heifers (AP), and hip height (HH) in Brahman cattle ...... 49

3-2. Environmental (co)variance estimates for scrotal circumference (SC),
age at puberty in heifers (AP), and hip height (HH) in Brahman cattle ...... 50

3-3. Genetic parameter estimates for scrotal circumference (SC),
age at puberty in heifers (AP), and hip height (HH) in Brahman cattle ...... 51

4-1. Least squares means SE for body condition scores (BCS) for first-,
second-, and third or greater-parity Brahman dams by frame size (FS) ..... 63

4-2. Least squares means SE for age at puberty (AP) by frame size (FS) and
body condition score (BCS) at 18 mo of age in Brahman heifers .......... 64

4-3. Least squares means SE for calving rate (CR) by frame size (FS) and
body condition score (BCS) for parity groups of Brahman cattle .......... 66

4-4. Least squares means SE for calving date (CD) by frame size (FS) and
body condition score (BCS) for parity groups of Brahman cattle .......... 68









4-5. Least squares means SE for survival rate (SR) by frame size (FS) and
body condition score (BCS) for parity groups of Brahman cattle .......... 70

4-6. Least squares means SE for weaning rate (WR) by frame size (FS) and
body condition score (BCS) for parity groups of Brahman cattle .......... 71

4-7. Least squares means SE for birth weight (BWT) by frame size (FS),
body condition score (BCS), and sex of calf (SEX) for parity
groups of Brahm an cattle ....................................... 73

4-8. Least squares means SE for weaning weight (WWT) by frame size (FS),
body condition score (BCS), and sex of calf (SEX) for parity
groups of Brahm an cattle ....................................... 75

4-9. Least squares means SE for preweaning average daily gain (ADG) by
frame size (FS), body condition score (BCS), and sex of calf (SEX)
for parity groups of Brahman cattle ................................ 77

4- 10. Least squares means SE for production per cow (PPC) by frame size (FS)
and body condition score (BCS) for parity groups of Brahman cattle ....... 78

5-1. Number of observations (n), means, standard deviations (SD), minimums,
and maximums for hip height (WHH; cm) and weight (WWT; kg) at
weaning, postweaning hip height growth (PHG; cm), and hip height
at 18 mo of age (HH18; cm) in Brahman cattle . . . . . . ...... 86

5-2. (Co)variance components and genetic parameters in a bivariate analysis
for hip height (WHH) and weight (WWT) at weaning in Brahman cattle .... 90

5-3. (Co)variance components and genetic parameters in a bivariate analysis
for weaning hip height (WHH) and postweaning hip height growth
up to 18 mo of age (PHG) in Brahman cattle . . . . . . ...... 93

5-4. Environmental and phenotypic (co)variances and correlations in bivariate
analyses for growth traits in Brahman cattle ..................... 94

5-5. (Co)variance components and genetic parameters in a bivariate analysis
for weaning weight (WWT) and hip height at 18 mo of age (HH18)
in B rahm an cattle ............................................. 96

5-6. Means, standard deviations, minimums, and maximums for direct and maternal
estimated breeding values (EBV) for hip height (WHH; cm) and
weight (WWT; kg) at weaning, postweaning hip height growth (PHG; cm),
and hip height at 18 mo of age (HH18; cm) of Brahman cattle (N = 1442) 100















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

ESTIMATION OF PHENOTYPIC AND GENETIC RELATIONSHIPS
AMONG HIP HEIGHT AND PRODUCTIVE AND REPRODUCTIVE PERFORMANCE
IN BRAHMAN CATTLE

By

Carlos A. Vargas L.

May 2000

Chairperson: T. A. Olson
Major Department: Animal Science

Covariance components for scrotal circumference at 18 mo of age (SC), age at puberty

in heifers (AP), and hip height at 18 mo (HH18); effect of small (SFS; 120 cm), medium (MFS;

130 cm), and large (LFS; 140 cm) frame size of heifer on age at puberty, and on subsequent

calving rate, calving date, survival rate, weaning rate, birth weight, preweaning ADG, weaning

weight (WWT), and kilograms of calf per cow exposed for first- (PID), second- (P2D) and

third or greater-parity (P3D) dams; and relationships between weaning hip height (WHH),

WWT, postweaning hip height growth (PHG), and HH18 were estimated in Brahman cattle.

Covariances were estimated using REML fitting multi-trait animal models. Least-squares

means estimated the effect of frame size on reproductive traits. Heritabilities for SC, AP, and

HH18 were .28, .42, and .65. Genetic correlations between SC and AP; SC and HH18; and









AP and HH18 were -.32, .19, and .25. Puberty occurred at younger ages in SFS and MFS

than in LFS heifers. Calving rates in P2D and P3D were less among LFS than among SFS.

Calf survival rate for PID was less for LFS than for SFS and MFS. Weaning rates in PID and

P2D were less for LFS than for SFS and MFS. Weaning weights of calves from PID and

P3D were heavier for LFS than for SFS. Heritabilities for WHH-, WWT-, PHG-, and HH18-

direct, and maternal averaged .69, .31, .13, .87; and .10, .18, .00, and .03, respectively.

Negative genetic correlations existed between direct and maternal effects for WHH, WWT,

PHG, and HH18. Selecting for increased SC favored earlier AP in heifers. Selecting for

HH18 may not adversely affect SC but might have some detrimental effect on AP in female

progeny. Females of SFS and MFS surpassed LFS by demonstrating earlier calving dates,

and greater calving, calf survival and weaning rates. There is a strong genetic relationship

between WHH and WWT that has an impact on HH18. Thus, if the breeding objective is to

manipulate growth to 18 mo of age, implementation of multiple trait breeding programs

considering WHH and WWT will aid in the prediction of hip height at time of selection.















CHAPTER 1
INTRODUCTION


A positive impact of the Brahman breed on beef production under subtropical and

tropical conditions has been well documented (Bonsma, 1973; Turner, 1980). However, a

negative impact on reproductive efficiency due to Brahman has been reported as compared to

Bos taurus breeds (Plasse, 1973; Martin et al., 1992). Because of this lowered reproductive

performance of Brahman cattle, their continued extensive use, either as a straightbred in tropical

environments to utilize their adaptation to adverse environmental conditions or as a crossbred in

subtropical environments to, in addition, gain the benefits of heterosis on growth and maternal

traits, may require an improvement in several reproductive traits.

The demand for faster gaining cattle with heavy yearling weights by the beef cattle

industry in the United States has greatly increased during the last thirty years. This trend was

due to the desire for a larger carcass and a leaner product as well as a more favorable dressing

percentage in larger type animals. The Brahman breed, characterized in the past by slow

feedlot growth, was affected by this trend. Because genes that affect growth have pleiotropic

effects on most other growth traits, selection for one growth-related trait causes correlated

responses in others. Consequently, selecting for faster growth rate and heavy body weights is

likely to result in an increase in frame size. Frame size was incorporated as a primary selection











objective in beef cattle for many years, and a frame score system was developed as an

indicator of growth or skeletal size of cattle (BIF, 1996). Frame score is a linear measurement

for hip height adjusted by the age of the animal.

Determining the optimum size in beef cattle has been of great concern in recent years

because selection for larger, faster gaining cattle and its association with increased mature body

size may be negatively affecting key reproductive performance traits. Body size can have both

biological and economic effects on the efficiency of beef production. Evaluation of the

phenotypic and genetic relationships of body size with biological effects such as maintenance

requirements, feed conversion, weight gains, milk production, reproductive performance, and

environmental adaptation, is critical in the design and application of effective selection programs

involving growth traits. The effect of size on reproductive performance in many studies has

been confounded with breed effects making it difficult to partition the variability into that due to

size and that due to breed differences. Thus, the evaluation of size and its effect on

performance traits within the Brahman breed will not only permit the characterization of size per

se, but also will allow for comparisons of productive and reproductive performance among the

different sizes without the confounding effect of breed composition.

Hip height is a trait easy to measure, is less susceptible to environmental variation (e.g.,

nutritional regimen, body condition or degree of fatness) than is body weight, and may better

reflect body size than does weight (Baker et al., 1988, Jenkins et al., 1991; Hoffman, 1997).

Also, mature hip height is reached earlier than is mature body weight. Hip height is a trait that is

correlated with many other traits. Several studies have shown strong phenotypic and genetic









3

associations between growth and reproductive traits in young females (Nelsen et al., 1982),

young bulls (Bourdon and Brinks, 1986), and mature females (Buttram and Willham, 1989).

Several studies have focused on the importance of management considerations for body

size and the occurrence of puberty in heifers (Lamond, 1970; Patterson et al., 1992). Baker et

al. (1988) demonstrated a high degree of interdependence among pubertal and growth

characters in cattle and concluded that height was an important source of variation for age at

puberty that should be considered in selection programs for reproductive traits. Thus,

characterization of the genetic effects of size on puberty in Brahman heifers should impact the

decision-making process relative to selection of a particular heifer size for specific nutritional

environments.

Hip height has been shown to be positively associated with scrotal circumference;

moderate and positive phenotypic and additive genetic correlations between hip height and

scrotal circumference have been reported (Kriese et al., 1991a; Smith et al., 1989c; Keeton et

al., 1996). Scrotal circumference has been described as an indicator of semen quality and

producing capacity, and as a useful trait for the prediction of age at puberty in bulls regardless

of age, weight and breed (Lunstra et al., 1978).

Although considerable emphasis has been placed on scrotal circumference and its

relationship to bull fertility, equally important is the relationship between scrotal circumference

and age at puberty in female progeny. Because larger selection differentials are possible in

males, selection response for early puberty in females can be enhanced by including scrotal

circumference as an indicator trait along with direct measures of age at puberty in females. The









4

value of scrotal circumference as an indicator trait for age at puberty in heifers relies on the

heritability of scrotal circumference and a favorable genetic correlation between both traits.

Thus, knowledge of the genetic relationships among measures of hip height and reproductive

traits in young animals is important to make effective management decisions for genetic progress

in Brahman cattle.

Selection of replacement heifers will affect the future productivity of the entire cow

herd. The effect of body size on different measures of female reproductive efficiency (e.g.,

calving and weaning rates, production per cow) assessed within a breed will aid in the

determination of the influence of selection for greater mature body size on total herd

productivity. Significant breedtype (size) x management interactions have been reported (Long

et al., 1979; Stewart et al., 1980; Buttram and Willham, 1989) that suggest that the size of the

animal and(or) breed of cattle to be produced under specific conditions, depends upon the type

of management implemented. Hence, determination of the effect of heifer body size on

subsequent reproductive performance within the Brahman breed will help to determine if there

are certain body sizes of Brahman cattle more suited to a specific environment.

Some characteristics are either difficult or expensive to measure or are expressed later

in life, after selection decisions have been made. Based on an association between size and its

influence on reproductive performance, determination of the genetic relationships between a

body size trait (e.g., height and/or weight) measured early in life, and a related trait measured

later in life (e.g., 18 mo of age) could facilitate the identification of a trait in young animals useful

to predict future productivity in mature animals. To effectively identify such an indicator trait, it











is important to ascertain the relative value of the additive genetic direct, additive genetic

maternal and correspondent genetic correlations among the traits involved. This information

would assist in the decision process and could lead to development of new selection strategies

for improving productivity in beef cattle.

Genetic parameter estimates for hip height and phenotypic and genetic relationships of

hip height with productive and reproductive performance traits are limited for Bos indicus and

Bos indicus derivative cattle raised under subtropical conditions. Therefore, the series of

studies in this dissertation are expected to accomplish the following objectives:

1) to estimate variance and covariance components, and genetic parameters among

scrotal circumference at 18 mo of age in bulls, age at puberty in heifers and hip height at 18 mo

of age in both sexes (Chapter 3);

2) to determine the effect of heifer frame size and fall body condition score on age at

puberty, and on subsequent calving rate, calving date, calf survival rate, weaning rate, calf birth

weight, calf weaning weight, preweaning average daily gain, and kilograms of calf per cow

exposed in first-, second- and third or greater-parity dams (Chapter 4); and

3) to estimate the direct genetic and maternal genetic effects for hip height and weight at

weaning, postweaning hip height growth, and hip height at 18 mo of age, to estimate genetic

correlations between weaning hip height and weaning weight, and between weaning hip height

and postweaning hip height growth, and between weaning weight and hip height at 18 mo of

age, and to examine the possibility of using estimated breeding values for height or weight at

weaning to predict performance for hip height at 18 mo of age in Brahman cattle (Chapter 5).















CHAPTER 2
LITERATURE REVIEW


Reproductive efficiency is the most economically important aspect of beef cattle

production. Beef cattle management decisions must be oriented to produce both males and

females that reach puberty at early ages and with high fertility rates. Reproductive efficiency in

Brahman has been reported to be inferior to that of Bos taurus breeds (Plasse, 1973; Martin et

al., 1992). The importance of body or skeletal size, and its effect on reproductive performance

has become a major concern due to the recent emphasis on a larger mature size.

Characterization of Brahman cattle for growth and reproductive traits, and their relationships is

limited. Thus, studies are needed to determine the relative influence of factors related to body

size that influence reproductive performance of Brahman cattle under subtropical conditions.

Hip height is probably the most convenient way of describing skeletal size in beef cattle;

it is a trait less susceptible to environmental variation than is body weight, and cattle reach their

mature height earlier than their mature body weight (Baker et al., 1988; Jenkins et al., 1991).

The Beef Improvement Federation (BIF, 1996) recommends that hip height be incorporated in

the national cattle evaluation. The American Angus Association provided yearling hip height

records in their Spring 1998 Sire Summary. Characterization of Brahman cattle for hip height,

as a measure of body size, and assessment of the phenotypic and genetic characteristics and









7

relationships of this growth trait to economically important traits related to male and female

productivity will help to determine its relative importance in the beef production process.


Genetic Parameters for Hip Height, Scrotal Circumference, and Age at Puberty


Genetic parameters are characteristics of the particular population and environmental

conditions under which they are estimated and as a result they may change over time due to

selection and management decisions (Falconer, 1989). Jenkins et al. (1991) have determined

that sufficient genetic variability, both between-breed and within-breed, for measures of growth

in beef cattle is available to allow the manipulation of growth characteristics through maturity.

Estimates of heritabilities and genetic correlations of growth and reproductive traits in beef

cattle are critical population parameters that are needed to design selection programs to

improve productivity of Brahman cattle.

Heritabilities

The strength of the association between phenotype (performance) and breeding value

for a trait in a population is defined as heritability. Heritability expresses the extent to which

phenotypes are determined by the genes transmitted from the parents. Thus, in animal

breeding, knowledge of heritability values is important to selection for polygenic traits, and for

prediction of breeding values and producing abilities. Heritability of a trait is not fixed. It may

vary from population to population and from environment to environment. Therefore, the

determination of corresponding heritability estimates for traits of economic importance in a











particular population would indicate the genetic progress expected from selection for

improvement of a particular trait in that population.

Hip height

Few reports of heritability estimates for hip height are available in the literature for Bos

taurus and Bos indicus derivative breeds (Table 2- 1). The magnitude of the heritability

estimates reported in the literature for hip height measured at different ages indicates that this

trait is largely under additive genetic control; that is, environmental effects contribute very little

to the phenotype. In mature cows of different breed composition, Jenkins et al. (1991)

reported a between-breed heritability estimate of .94 .28 for hip height, and a within-breed

estimate of .71 .12. In replacement heifers, Neville et al. (1978) reported heritability

estimates for hip height obtained by regression of daughter on dam of .54 .18 and .75 .16

from herds at Tifton, GA (Angus, Polled Hereford and 3/4 and 7/8 Simmental) and Reidsville,

GA (Angus, Polled Hereford and Santa Gertrudis), respectively. Fitting a sire model to a data

set from Brangus bulls, a yearling hip height heritability estimate of .27 was reported by Kriese

et al. (1991a). Bourdon and Brinks in Hereford bulls (1986) reported a heritability value of .43

.08 for hip height at weaning.

Scrotal circumference

Scrotal circumference is the most accurate predictor of age at puberty in males,

regardless of large differences in mature body weight and age at puberty among and within

different breeds of bulls (Lunstra et al., 1978; Lunstra, 1982), and it has a high positive












Table 2- 1. Heritability estimates for hip height, scrotal circumference, and age at
puberty in heifers

Parameter Breeda Value Reference


Hip Height
Weaning

Yearling



Maturity






Scrotal Circumference


HE

HE
HE
BA

BA
VB
VB
VB
VB

HE
HE
LI
HE
LI
AN
BA
AN
HE
AN
ZC
HE
HE
VB
VB
NE


HE
Age at puberty in heifers VB
HE
VB
VB
VB
VB
HE
VB
a Abbreviations are as follows: AN =


.43 + .08 Bourdon and Brinks, 1986


.55 + .08
.66
.27


.62
.94
.71 +
.54
.75


.53 + .06
.67
.39
.26 + .23
.46 + .05
.35 + .06
.16
.38+ .16
.41 + .06
.42
.26
.44 + .24
.41
.40 + .09
.39
.77


.20 + .16
.075
.48 + .18
.41 + .17
.61 + .18
.64 + .31
.10+ .17
.18 .11
.67 + .68
Angus, BA = Bi


Bourdon and Brinks, 1986
Kriese et al., 1991a
Kriese et al., 1991a

Choy, et al., 1996
Jenkins et al., 1991
Jenkins, et al., 1991
Neville et al., 1978
Neville et al., 1978

Bourdon and Brinks, 1986
Coulter and Foote, 1979
Keeton et al., 1993
King et al., 1983
Keeton et al., 1996
Knights et al., 1984
Kriese et al., 1991a
Latimer et al., 1982
Lunstra et al., 1988
Meyer et al., 1990
Meyer et al., 1990
Neely et al., 1982
Nelsen et al., 1986
Smith et al., 1989a
Smith et al., 1989c
Quirino and Bergmann., 1998

Arije and Wiltbank, 1971
Brinks, 1977
King et al., 1983
Laster et al., 1979
McNeil et al., 1984
Smith et al., 1976
Smith et al, 1989b
Toelle and Robison, 1985
Werre and Brinks, 1986


*angus, HE


Nellore, VB = Various Breeds, and ZC


= Hereford,
Zebu Cross


LI = Limousin, NE









10

genetic correlation with other measurements of reproductive performance in the male, such as

testes size and weight and sperm numbers (Neely et al., 1982; Palasz et al., 1994). Scrotal

circumference has been identified as the most appropriate male reproductive trait to be included

in multivariate genetic evaluations of Australian beef cattle (Meyer et al., 1990). Fields et al.

(1982) suggested that a large degree of variability in scrotal circumference and other

reproductive traits existed within the Brahman breed and that these differences might be

exploited in an attempt to increase reproductive efficiency.

Scrotal circumference is easy to measure and moderately to highly heritable: .44 .24

(Neely et al., 1982); .53 + .06 (Bourdon and Brinks, 1986); .39 (Smith et al., 1989c); and .40

+ .09 (Smith et al., 1989a). Kriese et al. (1991a) reported a higher heritability estimate for

scrotal circumference in a temperate than in a Brahman derivative breed, .53 for Hereford

versus .16 for Brangus. Similarly, Meyer et al. (1990) found heritability values of .53, and .42

for Hereford and Angus, respectively, and .26 for Zebu crosses. However, in the Nellore

breed, Quirino and Bergmann (1998) reported estimates of heritability for scrotal

circumference adjusted and unadjusted for body weight at 18 mo of age of .71 and .77,

respectively.

Heritability estimates of scrotal circumference reviewed by Brinks (1994) ranged from

.36 to .69 on an age and weight-adjusted basis. In his review, heritability values for scrotal

circumference adjusted for body weight differences (.44 to .69) appeared to be as highly

heritable as those values adjusted for age (.36 to .68), indicating that considerable additive









11

genetic variation exists for scrotal size relative to body weight or age. A summary of heritability

estimates for scrotal circumference is presented in Table 2- 1.

Age at puberty in heifers

Most of beef cattle management programs have as an objective to develop replacement

heifers such that they not only conceive early in their first breeding season but also that calve as

two-yr-olds. Therefore, management strategies for reducing age at puberty in heifers are

important to the economic efficiency of the cow herd. Brahman heifers reach puberty at an

older age when compared to heifers of Bos taurus breeds (Martin et al., 1992). They found

that within breed sources of genetic variation were large and important for age at puberty.

Thus, selection for reduced age at puberty should be successful in changing this trait.

Age at puberty in heifers generally has been reported as having a large environmental

and a low additive genetic variance. Most of the literature reports age at puberty in beef cattle

as a lowly heritable trait: .20 + .16 (Arije and Wiltbank, 1971); .075 (Brinks, 1977); .18 .11

(Toelle and Robison, 1985); and .10 .17 (Smith et al., 1989b). However, some authors

have reported moderate to high heritabilities for age at puberty: .64 .31 (Smith et al., 1976);

.61 .18 (MacNeil et al. 1984); and .67 .68 (Werre and Brinks, 1986). Nelsen et al.

(1982) estimated pubertal traits for a wide variety of cattle at one location and concluded,

based on breedtype differences, that selection among breeds, and perhaps within breeds,

should be successful in changing age at puberty. These reports indicate that the total amount of

available genetic variation for age at puberty in females may be high enough that progress could









12

be made through selection. Literature heritability estimates for age at puberty are summarized

in Table 2- 1.

Genetic Correlations

A genetic correlation represents the correlation between the additive breeding values

for two traits (e.g., age at puberty and scrotal circumference) or between the sum of additive

effects of the genes influencing both of the traits. Genetic correlations generally result from

pleiotropy, that is, groups of genes affecting more than one trait. Thus, if two traits are

genetically correlated, selection for one will cause genetic changes in the other. Furthermore,

the breeding value of one trait can be predicted based on the observed performance of another

trait that is genetically correlated with it.

The strength of the genetic association between growth and reproductive traits

measured in young animals will help to determine if selection for a growth character (e.g., hip

height) will cause any genetic changes in bull or heifer fertility. Furthermore, knowledge of the

magnitude and sign of the genetic correlation among traits can allow adequate selection

decisions to be made early in the life of the animal. Selection early in life should reduce costs

because reproductive traits are usually evaluated in females where they are more difficult to

measure and it takes long periods of time to measure.

The effects of growth on reproductive efficiency have been analyzed previously in

females (Smith et al., 1989c, 1989b; Buttram and Willham, 1989) and in males (Lunstra et al.,

1978; Bourdon and Brinks, 1986; Smith et al., 1989a, 1989c), but most of the work has been

done using measures of body weight, and with Bos taurus cattle.












Table 2-2. (Co)variance estimates for scrotal circumference and hip height

Parameter Breeda Value Reference


Additive genetic variance

Scrotal circumference (cm2)


Meyer et al, 1990
Meyer et al., 1991
Bourdon and Brinks, 1982
Kriese et al., 1991a
Keeton et al., 1996
Meyer et al., 1990
Meyer et al., 1991
Kriese et al., 1991a
Meyer et al., 1990
Meyer et al., 1991
Quirino and Bergmann, 1998


Hip Height (cm2)


0.9 Kriese et al., 1991a
0.6 Kriese et al., 1991a


Additive genetic covariance


Hip height and scrotal circumference
(cm x cm)


Environmental (co)variance

Scrotal circumference (cm2)


Hip height (cm2)


Hip height and scrotal circumference HE
(cm x cm) BA
aAbbreviations are as follows: AN = Angus, BA
NE = Nellore, VB = Various Breeds, and ZC =


0.6 Kriese et al., 1991a
0.2 Kriese et al., 1991a


Meyer et al., 1990
Meyer et al., 1991
Neely et al., 1982
Bourdon and Brinks, 1986
Kriese et al., 1991a
Meyer et al., 1991
Keeton et al., 1996
Kriese et al., 1991a
Meyer et al., 1990
Meyer et al., 1991
Quirino and Bergmann, 1998


0.50 Kriese et al., 1991a
1.59 Kriese et al., 1991a

0.18 Kriese et al., 1991a
0.47 Kriese et al., 1991a
= Brangus, HE = Hereford, LI = Limousin,
Zebu Cross











Hip height and scrotal circumference

Scrotal circumference is genetically and phenotypically correlated with important

growth traits used in beef selection programs. A positive association between postnatal growth

rate of progeny and scrotal circumference of sire has been reported (Smith, et al., 1989c).

Keeton et al. (1996) concluded that bulls that are genetically superior in scrotal circumference

should also be superior in the direct effect of preweaning growth.

Selection for scrotal circumference should not negatively affect additive growth traits.

Meyer et al. (1991) reported positive estimates of additive genetic covariances among growth

traits and scrotal circumference. These results indicated that information from the direct

measurements of growth traits and scrotal circumference augment each other when included in

a multiple trait genetic evaluation. (Co)variance estimates for hip height and scrotal

circumference are presented in Table 2-2.

The genetic correlations found by Bourdon and Brinks (1986) between 365-d body

weight and height and yearling scrotal circumference (.44 .16, and .40 21) indicate that

selection for increased growth to a year of age should increase scrotal circumference and vice

versa. Kriese et al. (1991 a) reported phenotypic correlations of .45 between yearling height

and scrotal circumference for Hereford and Brangus bulls and additive genetic correlations

between both traits of .36 in Hereford and .25 in Brangus. Lunstra et al. (1978) found that

scrotal circumference at puberty was relatively constant among breeds and across bulls differing

widely in age and body weight at puberty. Literature estimates for genetic and environmental









15

correlations for scrotal circumference, hip height, and yearling weights are presented in Table

2-3.

Hip height and age at puberty in heifers

Using a multiple regression and principal components analysis, Baker et al. (1988)

demonstrated a positive relationship between the growth rate of hip height and height of heifers

at puberty, concluding that height was an important source of variation for age at puberty. They

observed that increases in height of heifers through 15 mo of age were associated with younger

ages at puberty, and that increased growth rate for hip height was associated with heavier, taller

heifers at puberty. However, they did not find any significant relationship between age at

puberty and height at 360 and 450 days of age. Furthermore, their results from the second

principal components analysis indicated that heifers of the Brahman breed were relatively older

and larger at puberty.

Nelsen et al. (1982) concluded that under selection for age at puberty in heifers,

correlated changes would be expected in measures of size and growth. The genetic correlation

reported by Smith et al. (1989b) between yearling weight and age of puberty in heifers

(Hereford, Angus and Red Angus) was favorable but had a high standard error (-.14 +

.44). Estimates of genetic parameters for hip height, weight, and age at puberty in heifers are

presented in Table 2-3.

Lammond (1970) indicated that puberty in heifers can be expected to occur at a

genetically predetermined size and, only when they reach that weight can efficient reproductive

performance be obtained. The relatively greater reduction in genetic and phenotypic variation












for degree of maturity at puberty versus that at 365 and 550 days found by Smith et al. (1976),

suggested that puberty tends to occur at a constant fraction of mature weight.




Table 2-3. Genetic and environmental correlations estimates for scrotal
circumference, age at puberty in heifers, hip height and yearling weight

Parameter Breeda Value Reference
Genetic correlations


Scrotal circumference and
age at puberty

Scrotal circumference and
age at first breeding

Hip height and scrotal
circumference






Scrotal circumference and
yearling weight

Age at puberty in heifers
and yearling weight



Age and weight at puberty
in heifers


Environmental correlation

Hip height and scrotal
circumference


.71


.39


.42 .20
.36
.25
.39 .10
.51 .10
.17 .10


Brinks, 1977


Toelle and Robison, 1985


Bourdon and Brinks, 1986
Kriese et al., 1991a
Kriese et al., 1991a
Pratt et al., 1991
Pratt et al., 1991
Pratt et al., 1991


.10+ .11 Lunstra et al., 1988
.64 Quirino and Bergmann, 1998


-.17 .40
-.29
-.14 .44
-.25

.36
.42
.52 .23
.67 .24


Bourdon and Brinks, 1982
Smith et al., 1976
Smith et al., 1989b
Werre and Brinks, 1986

Arije and Wiltbank, 1971
Brinks, 1977
Laster et al., 1979
Smith et al., 1976


Bourdon and Brinks, 1986
Kriese et al., 1991a
Kriese et al., 1991a


a Abbreviations are as follows: HE = Hereford, AN


Angus, SM = Simmental,


BA = Brangus, VB = Various breeds, and ZC = Zebu Cross











Scrotal circumference and age at puberty in heifers

Because of the low heritabilities reported for most reproductive traits in beef females

(Bourdon and Brinks, 1982; Smith et al., 1989b; MacKinnon et al., 1990), little within breed

genetic improvement in reproductive efficiency through female selection is expected.

Furthermore, some reproductive traits in males tend to be moderately to highly heritable and

are either positively or not correlated with production traits (Coulter et al., 1976; Neely et al.,

1982; Toelle and Robison, 1985), suggesting that it may be more advantageous to select for

reproductive efficiency through male selection.

The key to genetic progress is selection. However, direct selection for female

reproductive performance can be applied only to females and the intensity of female selection

is usually low and occurs relatively late in life when the female has one or more records. Land

(1973) investigated the potential relationships between male and female reproductive activity in

two species, the mouse and the sheep. He concluded that male and female reproductive traits

are closely correlated genetically, and that this correlation may be mediated through several

similar physiological systems controlling reproductive functions in the male and female. Further

research in cattle support a strong relationship between male and female reproduction (Brinks

et al., 1978; MacKinnon et al., 1990; Meyer et al., 1991). This indicates that an indirect

approach to changing reproductive performance in females may be made by selecting for

reproductive traits in males.

Several studies in cattle have shown a high positive relationship between scrotal

circumference in males and age at puberty in females (Brinks et al., 1978; Lunstra, 1982; Smith









18

et al., 1989c). Toelle and Robison (1985) reported results that suggested that selection for

increased testicular size would lead to a decrease in age at first breeding in beef females.

Breeding for earlier age at puberty in females by selecting for larger scrotal circumference in

males was proposed by Martin et al. (1992); they concluded that age at puberty and scrotal

circumference are essentially the same trait because of the very strong genetic relationships that

exist between these traits.

Brinks (1977) reported a genetic correlation of -.71 between scrotal circumference in

bulls with age at puberty in their half-sib heifers. Lunstra (1982) reported a phenotypic

correlation of -.98 among breed means for scrotal circumference of yearling bulls with age at

puberty in heifers. Working with composite populations of nine parental beef breed groups,

Gregory et al. (1991) found a phenotypic correlation coefficient for age at puberty in heifers

with scrotal circumference of -.91. These results indicate that improved scrotal circumference

in bulls are associated with earlier ages at puberty in heifers. The coefficient for the regression

of age at puberty on scrotal circumference of sire (-.796 days/cm) reported by Smith et al.

(1989c), also indicates a favorable relationship between scrotal circumference of sires and age

at puberty in their female offspring. Meyer et al. (1991) found low but favorable estimates of

the genetic correlation between scrotal circumference and female fertility and concluded that

scrotal circumference can be used as an indicator of female reproductive performance,

recommending that it be included in a genetic evaluation scheme for Australian beef cattle.

Literature estimate values for genetic correlation between scrotal circumference and age at

puberty in heifers are presented in Table 2-3.









19

In addition to being a predictor of semen quantity and quality, selection for larger

scrotal circumference in herd sires seems to be an indirect method of selecting for younger age

at puberty in heifers. However, the amount of emphasis that should be given to scrotal

circumference as a male indicator depends on its heritability and genetic relationships with age

at puberty. Estimates of the relevant genetic parameters necessary to make selection decisions

based on scrotal circumference were not found in the literature for the Brahman breed.


Relationships Between Body Size and Performance in Females


The principal reason for maintaining a beef cattle operation is to profitably produce

calves. Efforts to increase productivity have emphasized increased weaning weights of the

calves. However, heavier weights at weaning have led to larger mature sizes in the cow herd.

This is a concern because there seems to be a negative relationship between mature size and

productivity (MacNeil et al., 1984; Buttram and Willham, 1989; Brown et al., 1997).

Productive efficiency of the beef cow is also associated with the animal's body reserves or fat

deposits. Body condition evaluation estimates subcutaneous fatty tissues in certain areas of the

animal body, and is a reliable and practical indicator of the nutritional status of the animal

(Richards et al., 1986). Body condition score has been shown to have an extremely important

effect on fertility rates in commercial beef cattle in Florida (Rae et al., 1993; Kunkle et al.,

1994).

Literature results in temperate breeds generally indicate a slightly negative to zero

(Bourdon and Brinks, 1982; Smith et al., 1989b); or positive (MacNeil et al., 1984) genetic









20

association between growth and fertility traits in beef cattle. In Zebu crosses, Meyer et al.

(1991) found estimates of low to moderate negative correlations (-.36 to -.66) between days

to calving and weights. However, some results indicate evidence that selection for growth traits

is not detrimental to reproductive traits in beef heifers (Wolfe et al., 1990), or in beef cows

(Meyer et al., 1991). MacKinnon et al. (1990) did not find a correlated response for

postweaning growth when selecting Droughtmaster cows for pregnancy rate. The influence of

growth on performance has been studied primarily in composite or crossbred populations

where it is difficult to determine whether differences were attributable to differences in size or to

breed composition (Olson, 1994). Thus, the evaluation of the effects of frame size on

reproductive efficiency independent of breed composition is of interest due to the great

variation in size in some breeds (Jenkins, 1991). Significant breedtype (size) x management

interactions have been reported and these results emphasize the importance of matching the size

and(or) breed of cattle to specific conditions and management systems (Stewart et al., 1980;

Buttram and Willham, 1989; Brown et al., 1997).

The relationship of nutritional management of the beef cow herd with reproductive

performance has been reviewed extensively (Long et al., 1979; Richards, et al., 1986; Vargas,

1994; Choy et al., 1996). Improper nutrition during the heifer development period may have

both short- and long-term negative effects on heifer productivity (Wiltbank et al. 1969; Stewart

et al., 1980; Ferrell, 1982; Patterson et al., 1992). Richards et al. (1986) concluded that body

condition at calving was the factor that had the greatest influence on interval from calving to first

estrus and on pregnancy rate of beef cattle.









21

Studies that evaluate performance of Brahman cattle of different growth potentials and

body condition scores under a similar management regime will contribute to improving our

knowledge about matching size to available resources and to predicting the ability of an animal

to adjust to prevailing environmental conditions.

Reproductive Performance

Attaining and maintaining good reproductive performance of the herd is a critical

determinant of economic efficiency in beef cattle. Economic losses associated with reduced

reproductive performance of females may be linked to older age at first calving, greater calf

mortality rates, reduced calf crop, increased culling, and less kilograms of calves sold.

Therefore, those factors that may have a negative influence on female reproductive traits need

to be identified and characterized, so that appropriate management decisions can be made.

Age at puberty

Age at puberty in heifers has a significant effect in determining reproductive efficiency of

the cow herd, especially when a restricted breeding season is utilized (Ferrell, 1982). When

heifers are bred to calve as two year olds, not only must they mate and conceive, but they must

do so early in the breeding season. Heifers that conceive early in the breeding season as

yearling tend to subsequently calve early and to produce more calves during their lifetime than

heifers that conceive later in the breeding season (Lesmeister et al., 1973). Similarly, females

calving for the first time as two year olds tend to have greater lifetime productivity than those

that calve for the first time as three year olds (Lee et al., 1982; Tran et al., 1988; Nufiez-

Dominguez et al., 1991).









22

Puberty in Bos indicus heifers has been reported to be attained at older ages than in

Bos taurus heifers (Plasse et al., 1968a; Galina and Arthur, 1989; Martin et al., 1992).

Averages of 816 d (Reynolds et al., 1963); 537 d (Baker et al., 1989); and 590 d (Plasse et

al., 1968a) have been reported for Brahman heifers in the Southern United States (Louisiana,

Texas and Florida), whereas in Argentina, an average age at puberty of 507 d was reported by

Mezzadra et al. (1993).

The influence of growth on puberty in beef heifers has been reported previously

(Wiltbank et al., 1969; Short and Bellows, 1971; Patterson et al., 1992). However, most

studies dealt with changes in body size through alteration of body weight via nutrition and(or)

breed composition. Increased pre- and postweaning weight gain has been reported to

decrease age at puberty in beef heifers (Arije and Wiltbank, 1971; Smith et al., 1976). Using

Brahman heifers in the llanos of Venezuela, Linares et al. (1975a) reported that the first

palpable corpus luteum occurred at an average age of 735 d and at 264.3 kg of body weight.

They concluded that the observed variation in growth rate variation only partially explained

differences in age at detection of the first corpus luteum. Nelsen et al. (1982) found that

Brahman heifers were the oldest (428 16 d), heaviest (287 10 kg), and tallest (122.4 1.3

cm) at puberty when compared in a five-breed diallel with the Angus, Hereford, Holstein, and

Jersey breeds and all possible two-breed crosses.

Age at puberty is affected by plane of nutrition (Grass et al., 1982; Patterson et al.,

1992; Schillo et al., 1992). Patterson et al. (1992) highlighted the importance of proper

nutritional status on the growing heifer and indicated that inadequate nutrition (under- or









23

overfeeding) may result in increased age at puberty, reduced conception rates, embryonic

mortality, and underdeveloped udders. In two experiments, Grass et al. (1982) found that in

general heifers fed diets high in energy were younger, heavier, had greater body condition

scores, and reached puberty earlier than heifers receiving the low energy diet. They concluded

that if attainment of puberty is dependent on body condition, level of nutrition could affect age at

puberty by influencing the time required to reach the necessary degree of fatness. In a study

designed to evaluate some factors affecting the onset of puberty in different breeds of cattle,

Ferrell (1982) reported that at 452 d of age heifer body condition score was not related to

heifer age at puberty, but it influenced the mean body weight at puberty.

Thus, characterization of Brahman cattle in terms of the relationship between age at

puberty and hip height as a measure of body size and body condition as an indicator of

nutritional status must be obtained to develop sound breeding programs for this breed.

Calving rate

Calving rate is usually defined as the percentage of cows exposed to breeding that

subsequently calved. It can be calculated as the product of cycling rate, conception rate and 1

minus the abortion rate. A calving rate of 75% was found in Brahman cows under stressful

conditions in the Venezuelan llanos (Linares et al., 1975b). Williams et al. (1990), in a

subtropical environment (Baton Rouge, LA, USA), reported an average calving rate of 62.0%

over four generations for Brahman cows. Tran et al. (1988) found a lifetime birth rate of 72%

in a purebred Brahman herd when comparing subsequent reproduction of heifers calving for the

first time at 2 vs 3 years of age. Calving rates obtained in straightbred Brahman heifers having









24

their first calving opportunity at 24, 30, and 36 mo of age, were 14, 12, and 56%, respectively

(DeRouen and Franke, 1989). The authors partially attributed this low performance to a

delayed onset of puberty and to an anestrus period exhibited by the Brahman breed. However,

a calving rate of 90 + 3.8% in Brahman cows has been reported in Florida (Peacock and

Koger; 1980).

In a study designed to evaluate three synthetic lines differing in mature size, Buttram and

Willham (1989) found that size was a significant source of variation for calving rate. Small

heifers had a greater calving rate (79.4%) than heifers from the large line (67.3%), and medium

size cattle ranked between them (76.0%). Line size also had a significant effect on calving rate

of second-parity and third-parity cows, where calving rate was greater in the small size line than

either the medium or large size line. They concluded that cows and heifers from the small line

were more efficient reproductively in terms of calving rate than those from the large line, and

that dams from the medium line generally ranked between both extreme size lines.

Body condition score has been used in beef cattle to predict the pregnancy rate

outcome, and to assess the nutritional management during gestation, such that management

decisions can be made in preparation for the subsequent breeding season. Richards et al.

(1986) concluded that body condition score at calving was the most important factor influencing

early return to estrus and pregnancy. Their results indicate that the likelihood of a range beef

cow of becoming pregnant when calving with a body condition score > 5 is greater than when

calving with a body condition score of < 4. In 8 commercial beef herds in Florida, Rae et al.









25

(1993) reported that cows having body condition scores at pregnancy examination of < 3 4,

and > 5 had pregnancy rates of 31, 60, and 89%, respectively.

Calving date

Using a restricted breeding season, early conception is a major component of high

fertility on a long term basis. Cows that conceive early also calve early in the calving season

increasing not only the probability of pregnancy in the subsequent breeding season, but also that

calves will be older and heavier at weaning (Laster et al., 1973; Azzam and Nielsen, 1987).

Cows that calve late in the calving season often do not return to estrus before the end of the

breeding season. Furthermore, Lesmeister et al. (1973) found that heifers calving earlier

tended to calve earlier throughout their lifetime. Thus, calving date should influence

reproductive performance of Brahman cattle. Calving date is ordinarily recorded as the number

of days from January 1 to the actual calving date or the day of birth using the Gregorian

calendar. In some cases the Gregorian date is used starting the count on the first day of the

event (e.g., calving season).

Brahman-sired heifers had the latest (63 3 d) calving dates when compared to

Angus- (45 2 d), Charolais- (50 2 d), and Hereford-sired (48 1 d) heifers (DeRouen

and Franke, 1989). Straightbred Brahman calves were born later (65.0 d) than Angus (45.0

d), Charolais (48.7 d), or Hereford (48.3 d) straightbred calves (Williams et al., 1990). The

observed difference in both studies is larger than the difference in gestation length of

approximately 11 days reported between Bos indicus and Bos taurus breeds (Plasse et al.,









26

1968b; Reynolds et al., 1980; Bourdon and Brinks, 1982), indicating that several factors may

be affecting this trait.

Growth traits may affect calving date. Birth weight of the calf is known to be the most

important factor affecting direct calving ease; as birth weight increases, calving difficulty

increases. Calving difficulty, in turn, did not affect pregnancy rate but did affect conception

date, thus increasing the interval from calving to conception (Colburn et al., 1997). Growth

traits such as weaning and yearling weights have been associated with earlier age at puberty

(Patterson et al., 1992), and earlier age at puberty is associated with earlier conception

(Byerley et al., 1987; Meyer et al, 1991). Meyer et al. (1991) reported estimates of

covariance components for days to calving and yearling and final weights in Zebu crosses in

temperate and tropical Australia. Days to calving is an alternative measure of reproductive

performance that represents the number of days from the first day of the breeding season to

calving, and thus, is related to conception date. Phenotypic correlations between body weights

and days to calving were generally negative but close to zero, implying little association between

the two traits, however, genetic correlations were negative and low to moderate (-.36 to

-.66). They concluded that joint selection for fertility and growth should improve genetic

potential in both.

Results in the literature indicate that to a large extent reproductive performance is

dictated by management (Martin et al., 1992; Patterson et al., 1992). However, environmental

effects may be associated with nutritional limitations based on body size. Large-framed heifers









27

experienced a reduction in reproductive performance that was attributed to their inability to

meet their nutritional requirements (Buttram and Willham, 1987; Brown et al., 1997).

Body fat reserves of beef cows at parturition influence early breeding in beef cows

(Richards et al., 1986; Selk et al., 1988; Randel, 1990). Body condition at calving is inversely

proportional to the length of the postpartum anestrus period in beef cows (Dziuk and Bellows,

1983). Within-class partial correlation coefficients (Selk et al., 1988), indicate that the number

of days from calving to conception of range beef cows was correlated negatively with

precalving body condition score change (-.25). Minimal precalving body condition losses

were associated with shorter periods from calving to next conception. Similarly, precalving

body condition score was negatively correlated with the number of days from calving to the

onset of ovarian luteal activity (-.18).

Thus, identification of factors influencing calving date, a satisfactory single measure of

female reproductive performance related to gestation length, birth weight and dystocia (Azzam

and Nielsen, 1987), would help in the development of new management strategies to increase

productivity in beef cattle.

Survival rate

Calf survival is defined as the percentage of calves born that survive to a specific age

(e.g., 24-, or 72-hours, a week, weaning age). Brahman calves have less survival to weaning

rates when compared to contemporary Bos taurus calves (Koger et al, 1967; Thrift, 1997). A

survival to weaning rate in Brahman calves of 85.8% compared to a 90% survival rate in other

breed groups was reported by Koger et al. (1967) in a study conducted in four experimental











stations in Florida. Brahman calves had a lower survival to weaning rate (84.3%) under

subtropical conditions (Louisiana) when compared to Bos taurus calves (Williams et al., 1990).

Comerford et al. (1987) reported a 24-hour survival rate in purebred Brahman calves of

86.0%.

Calf birth weight is related to calf survival to weaning age. Koger et al. (1967) found

that intermediate birth weights were associated with greater calf survival rates than either low or

heavy birth weights. Death losses were greater among the smaller Brahman calves than among

the smaller Angus calves at birth (Reynolds et al., 1980). Franke et al. (1975) identified a

health condition in up to 20% of Brahman calves associated with calves weighing 9.3 kg less at

birth than normal calves (25.8 kg). Because calves were observed to be in a weakened state,

they referred to this condition as weak calf syndrome. Birth weight is positively correlated to

postnatal growth rate (Garrick et al., 1989) and adult height (Jenkins et al., 1991), and,

therefore, it is expected that the effect of selection for mature growth on early growth traits,

including birth weight, in beef cattle may be partially responsible for greater death rates in

Brahman cattle.

Body composition pre- and(or) postpartum of beef cows can affect the cow's body

condition (Richards et al., 1986; Houghton et al., 1990), level of milk production (Shell et al.,

1995), and the immunoglobulin concentration in colostrum (Blecha et al., 1981; Shell et al.,

1995). Therefore, body composition influences the ability of calves to absorb immunoglobulin

from colostrum (Blecha et al., 1981), and the postnatal growth of their calves (Spitzer et al.,

1995). All of these factors can affect the health, growth, and survival to weaning of calves.









29

Thus, scoring body condition in the beef cow, which is a consequence of level of nutrition, can

be a practical and effective management tool to assess future performance of the calf.

Weaning rate

Weaning rate is defined as the product of pregnancy rate and survival rate to weaning,

usually based on the total number of cows exposed to breeding. Thus, factors related to

growth that affect either pregnancy rate or calf survival rate will be reflected in weaning rates.

Perozo et al. (1971) reported an average of 75% for weaning rate in a Brahman herd in

Turrialba, Costa Rica. In Beni, Bolivia, Plasse et al. (1993a) working with a Zebu herd of

Brahman and Nelore composition, found unadjusted and adjusted means for weaning rates of

62.1 + .60 and 71.1 + 1.7%, respectively. In purebred Brahman managed under more

favorable tropical conditions in Bolivia, Plasse et al. (1993b) calculated an unadjusted weaning

rate of 76.2%, and an adjusted weaning rate of 72.8%. Weaning rates for Brahman cattle in

the United States have been published: 69% (Peacock et al., 1971); and 63% (Tran et al.,

1988) in Florida; and 52.4% (Williams et al., 1990) in Louisiana.

Productive Performance

Profitability of beef cattle operations is assessed utilizing information on weights of

calves and production per year on a per cow basis (annual cow production). Low levels of

productivity must be improved if the producer is to stay in the beef cattle business. Therefore, it

is crucial to critically evaluate traits of economic importance and major factors affecting cow

performance to improve productivity and economic return on a per cow basis.











Birth and weaning weights and preweaning weight gains

In a Brahman herd under superior management in Bolivia, an average unadjusted birth

weight of 28.0 + .2 kg, and an average adjusted birth weight of 27.8 .3 kg were reported by

Plasse et al. (1993b). Average birth weights in Brahman calves reported for the United States

include: 28.4 kg (Plasse, 1979)in Florida; 28.9 + .7 kg (McElhenney et al., 1985) and 31.2

.6 kg (Browning et al., 1995) in Texas; and 29.7 + .6 kg in Georgia (Comerford et al., 1987).

An average unadjusted weaning weight of 161.7 kg has been published for a Brahman-

Nelore cow herd under tropical conditions (Plasse et al., 1993a). In a Brahman herd with

improved management in Bolivia, an average unadjusted weaning weight of 184.1 + 1.2 kg,

and an average adjusted weaning weight of 178.1 2.6 kg were reported by Plasse et al.

(1993b). Studies carried out in the United States reported average weaning weights in

Brahman: 180.0 kg as a summary of 19 publications (Plasse, 1979); 180.6 3.8 kg

(McElhenney et al., 1985) and 198.8 3.5 kg (Browning et al., 1995) in Texas; and 184.0 +

2.0 kg in Florida (Olson et al., 1981).

Reynolds et al. (1990), in a biological type x productivity study, mated dams to medium

and large size sire breeds, and found that there was a 4.3 kg difference in birth weight, and a

6.1 kg difference in 200-d weight between calves sired by the large and medium frame size sire

breeds. However, they concluded that not all genetic variation in the weight traits could be

explained by size of the sire breed and that using biological size as a major criterion for selecting

breeds to improve weaning weights of first-cross offspring would not be a sound management

procedure.









31

Cows allocated to three biological cow types (small, medium, and large) based on hip

height were evaluated in a four year study of their calf weaning traits (Brown et al., 1997).

Calves weaned from small cows were lighter than calves weaned from either medium or large

cows (192 vs 202 and 212 kg). However, the ratio of weight of calf to weight of cow

recorded at weaning, as an indicator of cow efficiency, was smallest for the large cows (.384)

when compared to the medium (.404) and small (.412) cows, that were not different. They

stressed the importance of matching cow body type to the environment.

Low productive efficiency in cows may be an additional consequence of an inadequate

postpartum energy status or inadequate body reserves necessary to meet their production

requirements. Richards et al. (1986) found that cows whose postpartum energy intake was

limited produced fewer kilograms of calf by weaning. Similarly, Kunkle et al. (1994) reported

that calves born to cows in body condition score 6 had greater preweaning average daily gains

(.841 kg) and heavier weaning weights (234 kg) than those born to cows in body condition

score 3 (.727 and 170 kg, respectively).

Production per cow

Weaning weight of calves produced per cow entering the breeding herd measures the

overall productive efficiency of the cow herd in a beef cattle operation. This index incorporates

the ability of a cow to conceive, calve, and wean a calf and allows cows to be compared based

on total production performance. In Turrialba, Costa Rica, Perozo et al. (1971) reported an

adjusted value of 138.5 kg for production per cow in a Brahman herd maintained on improved

pastures. Plasse et al. (1993a) found unadjusted and adjusted averages for production per









32

cow of 100.4 kg and 119.4 kg, respectively, in a Brahman-Nelore herd in Beni, Bolivia. In a

10 year study on Brahman cows introduced to Bolivia from Brazil and Florida, Plasse et al.

(1993b) reported an average weaning weight per cow in the herd of 135.7 kg. Kilograms of

calf produced per cow in the breeding herd is a complex trait that incorporates many traits of

the cow from conception to weaning, that are subject to diverse management and

environmental effects.

Greater body condition scores are related to greater pregnancy rates, shorter calving

intervals, older calf age at weaning, and greater calf daily weight gain (Richards et al., 1986;

Selk et al., 1988; Randel, 1990; Osoro and Wright, 1992), factors that determine the total

kilograms of calf produced per cow in the herd. Kunkle et al. (1994) evaluated the relationship

of body condition score to beef cow performance and income and found that cows in lower

body condition score have significantly lower income from calves produced. They concluded

that the increase in income from improving body condition score will vary in different situations

that need to be critically evaluated to decide on cost-effective management decisions.


Relationships Between Hip Height and Weight


Matching body size and resources plays a major role in establishing a beef production

system to optimize efficiency. Usually, body size assessment in beef cattle is based solely on

body weight and(or) weight gains. However, neither body weight nor weight gain as a single

selection criterion can account for all genetic differences in body size (Koots et al., 1994b).

Other traits also need to be considered to aid in the selection for body size. Hip height is a trait









33

that is easy to measure, it is not influenced by body condition or degree of fatness, it is directly

related to body size, and it has the additional advantage that it is related to female productive

and reproductive performance (Brown et al., 1997; Vargas et al., 1998, 1999).

The genetic evaluation of hip height and its relationships with weight should improve the

genetic evaluation for size and also aid in the selection for reproductive traits when these traits

are not incorporated in a multiple-trait evaluation. Estimates of heritability for various growth

traits are from moderate to high, indicating that, in general, these traits will respond to selection

(Mohiuddin, 1993). Similarly, genetic correlations among growth traits were positive and

moderate to high in magnitude in almost all studies reviewed by Mohiuddin (1993) and Koots

et al. (1994b). High and positive genetic correlations between traits of growth measured at a

fixed age (e.g., weaning) express the extent to which those measurements reflect what may be

genetically the same trait at that age. Furthermore, Koots et al. (1994b), based on the

magnitude of the genetic and phenotypic correlations found among different beef production

traits, suggested that ignoring associations among traits could lead to suboptimal selection

indexes and poorly designed breeding programs. Thus, it would be advantageous under some

circumstances to identify an indicator trait. Additionally, the existence of high and positive

genetic correlations between preweaning and postweaning growth traits (consecutive

measurements of the same trait) would make it possible to predict future performance at key

points in the productive cycle (e.g., 18 mo of age) based on measurements made at an early

age (e.g., weaning). Such predictions would be useful as early decisions on breeding programs

are of substantial economic value.









34

Maternal effects as components of growth in beef cattle have an important role in

animal breeding (Koch, 1972). Growth during the preweaning period is determined by the

innate genetic potential for growth in the offspring and by the maternal environment provided by

the dam through mothering ability and milk production during gestation and nursing. Maternal

effects are strictly environmental with respect to offspring, however, these effects can have both

environmental and genetic components with respect to the dam (Willham, 1972). The

existence of maternal additive genetic effects may bias estimates of direct additive genetic

effects because both are transmitted from one generation to the next. Thus, maternal effects

need to be considered in the analyses to obtain unbiased estimates of direct breeding values.

Furthermore, improvement of maternal response in addition to direct response can lead to

greater overall genetic progress. Genetic evaluation methods that separate direct and maternal

effects and evaluate their correlations help to achieve maximum genetic progress by increasing

the accuracy of selection (Baker, 1980; Robison, 1981). Furthermore, there is evidence of

strong maternal effects on postweaning growth traits (Mavrogenis et al., 1978; MacKinnon et

al., 1991; Meyer, 1992). Simultaneous estimation of these effects is possible with a model that

quantifies maternal effects and allows for their relationship with additive direct genetic effects

through the use of the genetic correlations (Henderson and Quaas, 1976; Quaas and Pollak,

1980).

The breeding value of an individual animal represents the genetic value of that individual

as a parent. Breeders try to choose as parents those animals with the best set of genes (i.e.,

those animals with the best breeding values). Therefore, prediction of accurate breeding values









35

of potential candidates for selection is required to decide on those individuals that will be

allowed to become parents of future generations. The strength of the relationship between

breeding values for one trait and breeding values for another trait is measured by the genetic

correlation between both traits. Thus, direct selection for one trait may cause a genetic change

in another. There are circumstances when it may be more practical and economical to select

for a correlated trait than to select directly for a trait of interest. Selection decisions for

replacement seedstock in Brahman cattle may be made at 18 mo of age. Early (i.e., at

weaning) and accurate prediction of performance at later ages (i.e., 18 mo) are of substantial

economic value to the beef cattle industry. Thus, knowledge of the relationship between

estimated breeding values for one trait measured early, and another trait measured at a later age

would not only facilitate the selection process, but it would be more rapid and economical.

Hip Height

Heritability estimates in the literature are limited for hip height in Brahman or Brahman

derivative cattle (Koots et al., 1994a, 1994b). Values reported in the literature (Table 2- 1)

range from moderate to high, indicating that this trait is largely under genetic control and that

improvement can be attained through selection. Accuracy of selection for traits with high

heritability values is maximized. Jenkins et al. (1991) reported a high within-breed heritability

estimate of .71 + .12 for mature hip height in cows. However, they concluded that the use of

records from mature animals, even though it would assure genetic progress, would also increase

the generation interval. The shorter the generation interval, the faster the genetic progress.

Selection applied in younger animals will aid in reducing the generation interval.









36

Use of hip height at weaning as an indicator trait for growth requires evaluation of its

genetic characteristics and genetic relationships with other measures of growth. Based on 29

published values, Koots et al. (1994a) reported an unweighted mean heritability and adjusted

standard error estimate of .61 .014, and a weighted mean heritability and adjusted standard

error estimate of .54 .31 for yearling hip height; an estimate of .43 .05 for both unweighted

and weighted mean heritability was the only value reported for hip height measured at weaning.

Information on the variance components due to direct genetic and maternal genetic effects for

hip height at weaning was not available in the literature searched.

Weaning Weight

Heritability estimates for weaning weight in Brahman for Latin America, Southern

United States, and Australia are presented in Table 2-4. A wide range of heritability estimates

(.06 to .47) with an average value estimate of .28 for weaning weight was reported by Plasse

(1979) for Brahman in Latin America.

Weaning weight in beef cattle is a maternally influenced trait and is affected by direct

and maternal genetic components (Cantet et al., 1988; Meyer, 1992; Robinson, 1996).

Therefore, knowledge of the magnitude of each effect and the degree of the relationship

between these components allows us to characterize weaning weight performance and assists in

designing selection procedures that will ensure the achievement of optimum genetic progress.

Limited information is available on direct and maternal genetic (co)variances for weaning weight

in Brahman cattle; estimates of the direct genetic and maternal genetic effects ranged from .23

to .64, and from .04 to .16, respectively (Mohiuddin, 1993).












Table 2-4. Heritability estimates for weaning weight in Brahman cattle and Bos
indicus crosses by geographical region

Parameter Breeda Value Reference

Latin America BR .18 Hernmndez, 1977
BR .47 .18 Hinojosa and Valera-Alvarez,1976
BR .28b Plasse, 1979

United States BR .23 Kriese, et al., 1991b
BA .21 Kriese, et al., 1991b
BM .21 Kriese, et al., 1991b
SG .25 Kriese, et al., 1991b
BR .29 Elzo and Wakeman, 1998
ZC .10 Elzo et al., 1998
BR .13 .03 Pacho, 1981
BR .12 .05 Pacho, 1981

Australia ZC .20 + .07 MacKinnon et al., 1991
BR .35 .11 Robinson and Rourke, 1992
BR .64 .18 Robinson and Rourke, 1992
ZC .33 .11 Robinson and Rourke, 1992
a Abbreviations are as follows: BR = Brahman, BA = Brangus, SG = Santa
Gertrudis, BM = Beefmaster, and ZC = Zebu Cross
b Average of 12 estimates reported by Plasse (1979)




Koots et al. (1994a) provided weighted mean heritability estimates for direct and

maternal effects for weaning weight of .24 and .13, and unweighted mean estimates of .27 and

.20, respectively. Using an animal maternal model on 200-d weaning weight data from two

Australian Brahman herds, Robinson and Rourke (1992) reported values of .35 and .52 for

direct and .04 and .07 for maternal effects. These additive and maternal heritability values

indicate that weaning weight of a calf is more determined by its own genetic ability for growth

than by the genetic characteristics of the dam.









38

Weaning weight direct-maternal genetic correlations are reported as negative for most

beef breeds (Meyer, 1992; Pollak et al., 1994). However, some studies suggest that such

negative correlations are a consequence of other effects in the data, rather than evidence of a

true negative genetic relationship (Willham, 1972; Koch, 1972; Cantet et al., 1988; Meyer,

1992; Robinson, 1996). Several studies suggest the possibility of the existence of a negative

environmental covariance between the dam and offspring that may bias the estimates of the

direct-maternal genetic correlation downwards (Cantet, 1988; Meyer, 1992). Meyer (1992)

suggested that the negative direct-maternal correlation for weaning weight of -.78 obtained

with Zebu cross data, may be the result of a negative influence of the maternal environmental

effects of the dams (e.g., over-feeding) on their daughters. Meyer (1992), considering a subset

of Zebu cross data (Africander-Brahman cross), identified a moderate and negative direct-

maternal genetic correlation of -.26. Estimates of direct-maternal genetic correlations for

weaning weight have been found to differ among pure breeds by magnitude and more

importantly, by sign (Van Vleck et al., 1996). The genetic correlation between 205-d weaning

weight direct and maternal reported for Brahman cattle by Kriese et al. (1991b) was small and

positive (.15). This is in contrast to the negative and moderate in magnitude estimates found in

the same study in Brangus (-.23) and Santa Gertrudis (-.43) cattle; while that for Beefmaster

was small and negative (-.06). Elzo et al. (1998) reported a direct-maternal correlation

estimate for weaning weight in Brahman cattle of -.50.

High and positive pooled genetic correlations between consecutive measurements of

body weights (e.g., .86 coefficient between 200-d and 550-d weights) reported by Robinson









39

and Rourke (1992) for Brahman and Zebu crosses indicate that it is possible to make breeding

selection decisions regarding growth at later ages based on information from younger animals.

Hip Height and Body Weight Relationships

Growth traits in beef cattle are interrelated, and no single character can be fully

understood without some consideration of the others. Phenotypic relationships between height

and weight parameters in cattle have been analyzed (Nelsen et al., 1982; Jenkins et al., 1991;

Heinrichs et al., 1992). In dairy cattle, Heinrichs et al. (1992) showed wither height to be

highly related (R2 > .95) to body weight and suggested that in circumstances for which body

weight could not be obtained, height could be used to quantify growth. In beef cattle, Nelsen et

al. (1982) analyzed the relationships between weight and hip height measured from 9 through

66 mo of age in a five-breed diallel that included the Brahman breed. They reported

phenotypic correlations between mature height and weight of .67, and between maturing rates

for height and weight of .48 for Brahman cattle that indicated strong across-trait positive

relationship between measures of size, and between maturing rates for both traits. They also

observed that the weight to height relationship over the range of ages analyzed seemed to be

linear; and estimated a regression coefficient of 10.51 + .29 kg/cm for weight on height. They

concluded that definite genetic influences on growth patterns (e.g., fat deposition, muscle and

bone growth) could be implied based on the different weight to height relationship parameters

obtained within the different breedtypes studied. Beef production efficiency could also be

improved through crossbreeding by properly utilizing genetic differences among breeds in

growth rate and mature size (Smith et al., 1976). However, to take advantage of these









40

differences requires characterization of patterns of growth and of genetic relationships among

measures of growth for various breeds (e.g., Brahman).

Few genetic estimates are reported in the literature on the relationship between height

and other growth traits in beef cattle. Unweighted mean genetic correlations (number of

estimates) among yearling height and weaning weight direct, weaning weight maternal, weaning

gain direct, yearling weight direct, and yearling gain direct published by Koots et al. (1994b)

were, respectively, .53 (3), -.29 (2), .28 (2), .40 (8), and .54 (1). It appears from these

estimates that height and weight are affected by the same group of genes indicating that

appropriate selection for one trait will change the other. This relationship seems desirable

because a selection program based on increased hip height will improve weight. Thus, if

weaning body measures for growth can be accurately used to predict subsequent performance,

evaluations of growth potential in young animals would improve and the decision-making

process would be more effective.

Best linear unbiased prediction breeding values based on the animal model (Quaas and

Pollak, 1980) are preferred today to rank animals for selection. Thus, predicted breeding

values are required for those animals that are to become parents. The effectiveness of selection

depends on the quality of such predictions. Thus, evaluation of correlations between accurately

estimated breeding values for hip height and weight that will provide a better understanding of

the effects of using hip height and/or weight measured at weaning on hip height measured at 18

mo of age will determine how to apply an effective selection program.









41

Turner (1980) presented a comprehensive review on the genetic and biological aspects

of Bos indicus cattle adaptability to environmental stresses. He concluded that compared to

Bos taurus cattle, the unique abilities of Bos indicus to be heat tolerant by maintaining thermal

equilibrium, to be more tolerant to ecto- (flies, mosquitos, ticks), and endo-parasites, and to

utilize forages more efficiently, are some of the reasons why Zebu cattle have contributed

significantly to beef cattle production as purebreds in tropical conditions and in crossbreeding

programs in subtropical conditions. However, recognition of problems in Bos indicus cattle

related to reproductive efficiency (late puberty, low ovulation rates, delayed estrus), and to

preweaning and postweaning growth performance (lack of vigor at birth, slow-growing, fewer

high grading carcasses, and less tender beef), both indicators of functional efficiency and of

adaptation to the environment, have been related to body size. Natural selection for fitness

traits tends to favor relatively small size genotypes and artificial selection for production traits

favors relatively large size genotypes (Fitzhugh, 1986). Thus, to match cow size to the

production environment requires first the characterization of the production-market

environment, second, the characterization of the specific breed for growth and reproductive

traits, and finally an evaluation of their relationships. This will ensure that the match is both

technically and economically feasible.















CHAPTER 3
ESTIMATION OF GENETIC PARAMETERS FOR SCROTAL CIRCUMFERENCE,
AGE AT PUBERTY IN HEIFERS, AND HIP HEIGHT IN BRAHMAN CATTLE


Introduction


Age at puberty in heifers can have a major effect on the efficiency of the beef cattle

enterprise when heifers are bred to calve first as 2 yr olds, especially under a restricted

breeding season. Brahman heifers reach puberty at an older age when compared to heifers of

Bos taurus breeds (Martin et al., 1992). Martin et al. (1992) attributed average differences for

age at puberty between breeds to the additive effects of genes present in diverse frequencies

within breeds.

Even though considerable emphasis has been placed on scrotal circumference and its

relationship to bull fertility (Lunstra et al., 1978), the relationship between scrotal circumference

and reproduction in female progeny is equally important (Brinks, 1977; King et al., 1983).

Because larger selection differentials are possible in males, selection response can be enhanced

by including scrotal circumference as an indicator trait along with direct measures of age at

puberty in females. Several studies (Brinks et al., 1978; Toelle and Robison, 1985; Martin et

al., 1992) have reported favorable genetic relationships between reproductive traits in bulls

(e.g., scrotal circumference) and females (e.g., age at puberty).









43

Favorable genetic correlations between reproductive and growth traits in beef cattle

have been reported (Wolfe et al., 1990; Meyer et al., 1991). Baker et al. (1988)

demonstrated a high degree of interdependence among pubertal and growth characters in cattle

and concluded that height was an important source of variation for age and weight at puberty.

They indicated that because height is less susceptible to environmental variation than weight and

mature heights are reached earlier than mature weights, height should be considered in selection

programs for reproductive traits.

Thus, the objective of this study was to estimate covariance components and genetic

parameters among scrotal circumference (SC) in Brahman bulls, age at puberty (AP) in

Brahman heifers and hip height (HH) in both sexes.


Materials and Methods


Data Description and Animal Management

Data were collected from Brahman cattle between 1984 and 1994 at the Subtropical

Agricultural Research Station (STARS) located near Brooksville, Florida. The geographical

coordinates of STARS (Main Station) are 280 37' 00" north latitude and 820 21' 30" west

longitude. Average annual rainfall is 1,372 mm and over half falls in June, July, August, and

September. Average year-round temperature is approximately 22C with occasional frosts

occurring from November through March.

The Brahman herd at STARS used in this study was composed of purebred and

upgraded cattle. Grade cattle descended from Brahman-sired cows, with at least two-thirds









44

Brahman breeding, upgraded two or three additional generations. Complete pedigree records

relating all animals to the base herd were available. The number of sires used per year ranged

from two to five. To maintain connectedness of the data across years, up to three sires were

used in two consecutive years. Mating was not random. An assortative mating based on

observed HH was practiced, mating groups were formed such that dams and sires were of

comparable heights. The total number of sires and dams that had offspring with records were

28 and 261, respectively. The number of records per trait were 684 HH, measured on heifers

and bulls at 18 mo of age (BIF, 1996), 287 SC, measured in bulls at 18 mo of age (BIF,

1996), and 292 AP, measured only in heifers.

Calves were born from late December to early April. Calves remained with their dams

on bahiagrass (Paspalum notatum) pastures until weaning in September, when calves were

grouped by sex, and fed a commercially prepared, medicated supplement (65% TDN, 14%

CP, plus antibiotics) for approximately 1 mo. Heifers were fed .91 to 2.27 kg/d of concentrate

(depending on the year) and 1.81 kg/d molasses (1993 to 1995), and hay (bahiagrass,

perennial peanut, or Alyce clover) was provided for ad libitum intake during winter until spring

of the following year when growth of bahiagrass pasture was adequate to support the heifers.

Bulls were fed 4.54 kg/d of concentrate, and bahiagrass hay was offered for ad libitum intake

during periods of low forage availability (bahiagrass) for about 1 yr after weaning. As heifers

approached 2 yr of age, during their second winter, they were given free access to bahiagrass

hay and 1.81 kg/d of molasses. All cattle had free access to minerals year round.









45

Age at puberty was defined to be the age (days) at first detected ovulatory estrus

(Senseman, 1989). The procedure used to determine this ovulatory estrus was somewhat

different in the first period (1984 to 1988) and in the second period (1989 to 1994) of this

study. In both periods, estrus was detected in heifers from 10 to 24 mo of age by visual

observation with the aid of bulls (sterile in Period 1, and fertile in Period 2) with chin ball

marking devices. However, different procedures were used in Periods 1 and 2 to ascertain the

occurrence of the first ovulatory estrus. In the Period 1, when estrus was observed, the first

ovulatory estrus was considered to have occurred when 1) a corpus luteum was detected by

rectal palpation (1984, 1987, and 1988) or 2) a corpus luteum was detected by rectal

palpation, and the concentration of plasma progesterone was greater than 1 ng/mL measured

by RIA (1985 and 1986). These tests (rectal palpation and progesterone concentrations) were

conducted every 28 d. When estrus was not observed, but luteal tissue was present, and(or)

plasma progesterone was greater than 1 ng/mL, the date of puberty was estimated to be 14 d

preceding the palpation. In Period 2 the bulls used for estrus detection were fertile. Thus,

these bulls were not only used for estrus detection, but also for the detection of the first

ovulatory estrus by allowing them to impregnate heifers. Here, the day of the first ovulatory

estrus was assumed to be the day a heifer became pregnant. Pregnancy status was checked

every 28 d, and fetal age was determined from fetal size by rectal palpation. The date at first

ovulatory estrus was determined based on fetal age and estrus detection data. The accuracy of

detection of the first ovulatory estrus by the procedures used in Periods 1 and 2 was assumed

to be similar.











Statistical Analysis

The genetic relationship was complete for the animals evaluated in this study. Thus,

changes in variances and covariances that might have occurred as a result of the assortative

mating would not affect the relationship matrix (Sorensen and Kennedy, 1984; Fernando and

Gianola, 1990; Henderson, 1990). The data were analyzed using a multiple trait animal model

(Henderson and Quaas, 1976). Hip height, SC, and AP were the traits considered. Hip height

was measured in both sexes. Age at puberty was measured on females and SC on males.

Fixed effects considered were different for each trait, in the SC model were included year of

birth (YOB) and age of dam (AOD) as well as age at measurement (AGE) as a linear

covariate. Fixed effects fitted to the AP model were YOB and AOD. Fixed effects in the HH

model were YOB, sex, and AOD as well as AGE as a linear covariate. No adjustment to

either trait was made before analysis. Random effects in the model were animal and residual.

The AP in heifers and SC were connected through the numerator of the relationship matrix and

the matrix of genetic covariances among traits. The full relationship matrix between animals was

included by incorporating all pedigree information. The form of the three-trait animal model

(Appendix A) followed that of Henderson and Quass (1976). The variance of the animal

effects [ V(u) ] was A x Go, where A is the numerator relationship matrix among all animals


and Go is the additive genetic covariance among the three traits. The variance of the residual

[ V(e) ] was I x Ro, where












ril 0 r,
Ro = 0 r22 r2,
r.1 r.2 r,


The covariance between SC and AP is zero because these are sex-limited traits (i.e., measured

in animals of different sex); thus, no environmental covariance exists between SC and AP.

Thus, the (co)variance parameters to be estimated were three additive genetic variance

components (2 072 and ao2 ), three additive genetic covariance components between

them (a A and O A ), and five residual error (co)variances ( 2 2 2 e ,

023 ). Genetic parameters were estimated for SC, AP, and HH. Heritabilities for each trait

and the genetic and environmental correlations between them were also computed.

Analyses were carried out using multiple trait derivative-free restricted maximum

likelihood (MTDFREML, Boldman et al., 1995). The strategy for estimation of (co)variances

with multiple traits was as follows: 1) starting values for the estimates of variance components

for the three traits were obtained by fitting a single trait animal model for each trait; 2)

multivariate estimation was initiated with a cold start holding the variance estimates from single

trait analyses constant, using guessed covariances as starting values and a low level of

convergence criterion of 10 3; 3) a cold restart from apparently converged estimates

considering all parameters in the model simultaneously was run using the same low level of

convergence as in the previous step; 4) cold restarts, maintaining the convergence criterion of

10 3, were repeated until -2 log likelihood did not change in the first two decimal positions; 5)

a cold restart was run at a high level of convergence 10 9; and 6) to check for convergence to a









48

local rather than to a global maximum, a cold restart from previous converged estimates at a

high level of convergence was repeated until the smallest -2 log likelihood was found. Changes

in -2 log likelihood beyond the third decimal position were considered not important.


Results and Discussion


Heritabilities

Estimates of additive, environmental (co)variance components and genetic parameters

are presented in Tables 3- 1, 3- 2, and 3- 3, respectively. The estimate of heritability for SC

was .28. Scrotal circumference has been reported as moderately to highly heritable in

temperate and low to moderately heritable in tropical cattle. Estimates for Bos taurus breeds

range from .41 to .53 for Hereford (Lunstra et al., 1988; Meyer et al., 1990; Kriese et al.,

1991a) and from .36 to .42 for Angus (Knights et al., 1984; Meyer et al., 1990). Reported

heritability estimates for SC in Brangus (Kriese et al., 1991a) and Zebu crosses (Meyer et al.,

1990) were .16 and .26, respectively. The magnitude of the estimate found in the present study

suggests that improvement in SC can be achieved by selection within Brahman cattle.

The estimate of heritability for AP was .42. Similar estimates were reported by Laster

et al. (1979) and Splan et al. (1996) in Bos taurus crossbred heifers (.41 and .43, respectively)

and King et al. (1983) in Hereford heifers (.48). A pooled estimate of .61 in crossbred heifers

from straightbred Hereford and Angus cows mated to Hereford, Angus, Jersey, South Devon,

Limousin, Charolais, or Simmental sires was reported by McNeil et al. (1984). Lower

estimates were reported in Hereford, Angus, and Red Angus cattle (.20, Arije and Wiltbank,









49

1971; .10, Smith et al., 1989b). Based on this result, a selection program for early age at

puberty in Brahman heifers should result in improvement for the trait.



Table 3 -1. Additive genetic (co)variance estimates for scrotal
circumference (SC), age at puberty in heifers (AP), and hip height (HH)
in Brahman cattle

Traits
Traitsb
SC AP HH

Scrotal circumference 2.5 -31.5 1.3
Age at puberty 3,863.6 70.1
Hip height 19.6

aVariances in the diagonal; covariances above.
bScrotal circumference and hip height in centimeters and age at
puberty in days.



Hip height is probably the most convenient way of describing skeletal size in beef cattle.

Heritability for hip height was .65. Most literature reports of heritabilities for HH are moderate

to high. Neville et al. (1978) reported pooled estimates for HH in replacement heifers of .54

and .75 in herds at Tifton, GA (Angus, Polled Hereford, and upgraded Simmental) and

Reidsville, GA (Angus, Polled Hereford, and Santa Gertrudis), respectively. In Hereford bulls,

hip height heritabilities estimates were .55 (Bourdon and Brinks, 1986) and .66 (Kriese et al.,

1991a). In the Brangus breed Kriese et al. (1991a) and Choy et al. (1996) reported

heritabilities estimates of .27 and .62, respectively.











Table 3-2. Environmental (co)variance estimates for scrotal
circumference (SC), age at puberty in heifers (AP), and hip height (HH)
in Brahman cattle

Traits
Traitsb
SC AP HH

Scrotal circumference 6.4 1.4
Age at puberty 5,422.2 -50.3
Hip height 10.5
aVariances in the diagonal; covariances above.
bScrotal circumference and hip height in centimeters and age at
puberty in days.


Genetic Correlations

Genetic correlations between SC and AP, SC and HH, and between AP and HH are

presented in Table 3-3. The estimate of the genetic correlation obtained between SC and AP

in heifers (-.32) was favorable, which indicates that heifers that reach puberty earlier were

genetically associated with bulls of large scrotal circumference at 18 mo of age. Brinks et al.

(1978) reported a negative (favorable) genetic correlation of -.71 between SC in bulls with AP

in their half-sib sisters. Similarly, the regression coefficient of AP on SC (-.796 d/cm) reported

by Smith et al. (1989c) and the phenotypic correlations of -.98 (Lunstra, 1982) and -.91

(Gregory et al., 1991) have also indicated a favorable relationship between SC and AP in

heifers. Even though no comparable values were found for the Brahman breed, Meyer et al.

(1991) with Zebu crosses and MacKinnon et al. (1990) with Droughtmaster (Brahman x

Shorthorn) cattle found low but favorable estimates for the genetic correlation between SC and









51

female fertility (pregnancy rate and days to calving), and they concluded that SC could be used

as an indicator trait of female reproductive performance. Toelle and Robison (1985), using

Hereford females, reported a genetic correlation of age at first breeding with yearling SC of

-.39, which also supports the assertion that selection on scrotal circumference would be

effective in decreasing age at puberty in heifers. Even though a higher heritability value was

found for AP than for SC, the favorable genetic relationship between SC and AP found here

indicates that it might be possible to achieve more rapid progress in AP under indirect selection

for SC than from selection for AP itself, because AP is very labor- intensive and difficult to

measure directly and with precision.




Table 3 -3. Genetic parameter estimates for scrotal circumference
(SC), age at puberty in heifers (AP), and hip height (HH) in Brahman
cattle

Traits
Traits
SC AP HH

Scrotal circumference .28 -.32 .19
Age at puberty .42 .25
Hip height .19 -.13 .65

aHeritabilities in the diagonal; genetic correlations above;
environmental correlations below.



The additive genetic correlation estimate between SC and HH at 18 mo of age was

positive and low in magnitude (.19). This result is somewhat lower than reported estimates in









52

the literature. In Hereford bulls, higher positive genetic correlations between SC and HH have

been reported, .42 (Bourdon and Brinks, 1986) and .36 (Kriese et al., 1991a). However, in

Brangus, Kriese et al. (1991 a) found a positive genetic correlation between SC and yearling

HH of a magnitude similar to the one found here (.25). Pratt et al. (1991) reported phenotypic

correlations between SC and HH in Zebu-derived breed bulls, predominantly Santa Gertrudis.

Their analysis was performed with two data sets that differed in test entry requirements and

feeding management. Estimates of correlations at the end of the 140-d gain test were .09 and

.61 for data sets 1 and 2, respectively. The favorable genetic correlation obtained in the

present study indicates that selecting for SC may change the growth curve of bulls or vice versa

(i.e., selecting for increased hip height at 18 mo of age should increase scrotal circumference).

The estimated genetic correlation between AP and HH of .25 found in this study

supports the existence of an unfavorable genetic correlation between the component trait of

growth and the component trait of female reproductive performance studied. Although low in

magnitude, this association of hip height and age at puberty in heifers indicates that selection in

Brahman cattle for increased HH of heifers at 18 mo of age should result in heifers that are

taller and older at puberty. This relationship is in contrast to the positive genetic correlation

found between HH and SC in bulls. Thus, because selection for large SC may result in the

selection of taller bulls, culling of bulls with extreme hip heights will be an adequate selection

criterion.

Previous studies have shown that within a breed, growth rate had no significant effect

on age at puberty in heifers (Laster et al., 1979; Nelsen et al., 1982). Wolfe et al. (1990),









53

when evaluating three Hereford lines selected for weaning weight, final yearling weight, and final

weight plus muscling score, concluded that selection for growth did not have a detrimental

effect on age at puberty in heifers. Similarly, Baker et al. (1988), when analyzing puberty and

growth relationships in cattle, concluded that differing growth rates due to genetic potential did

not affect age at puberty to any significant extent and that the same concept would apply to the

relationship between weight at puberty and growth rate for weight. However, they reported

that growth rate for height affected weight and height at puberty. Thus, increased growth rate

for hip height was associated with heavier, taller heifers at puberty. They found, after

adjustment for breed-type and management, that taller heifers at 315 d of age were older at

puberty with a regression coefficient of 2.04 d/cm and that hip height at 360 d of age was not a

significant source of variation for age at puberty. Their results indicated that the majority of the

variation among breed-types was due to height and made conclusions about the need to

consider all pubertal characters in a simultaneous manner in order to have a full understanding

of their relationships. Genetic correlations reported by Bourdon and Brinks (1982) and Smith

et al. (1989b) between yearling weight, as a measure of size, and age of puberty in heifers were

favorable ( -. 17 .40 and -. 14 .44, respectively) but had high standard errors.

Because limited effort has been directed toward estimating genetic parameters in Bos

indicus and Bos indicus derivative breeds, such as the Brahman, variances and covariances

estimated in this study should be useful in future Brahman breed genetic evaluations. Even

though the estimates of genetic parameters obtained were within the range of published values

for these traits, standard errors are expected to be large because the data set was small and









54

unbalanced. However, genetic and environmental covariances among traits were included in

the three-trait model, so records for one trait had an impact on evaluations for the other traits.

Furthermore, estimating covariances when traits are correlated uses information from all traits to

estimate all covariances, and thus increases the accuracy of estimation of all of them. Even

though caution should be exercised when interpreting the results obtained, the magnitude of the

estimated additive genetic variability suggests that progress could be made through selection.

Results showed evidence of a favorable genetic relationship between scrotal circumference in

bulls and age at puberty in heifers under subtropical conditions. There was also evidence that

selecting bulls for hip height would not adversely affect reproduction in males but would have

some detrimental effect on females. Even though management practices can be used to

decrease age at puberty in heifers (e.g., increasing growth rate as a function of nutrition), it is

important that the animals have the genetic potential to express early puberty.


Implications


A favorable genetic association seems to exist between scrotal circumference in bulls

and age at puberty in heifers. Thus, selection of Brahman sires for increased scrotal

circumference at 18 mo of age should provide a useful means for making genetic progress in

reducing age at puberty of heifers. Scrotal circumference thus serves as an indicator trait to

indirectly select for early age at puberty in heifers. Because an unfavorable genetic correlation

between hip height at 18 mo and age at puberty in heifers was identified in this study, selection









55

programs in Brahman cattle should be planned taking into consideration growth measurements

and reproductive traits simultaneously.

Summary


Genetic parameters were estimated for scrotal circumference (SC; n = 287), age at

puberty in heifers (AP; n = 292), and hip height in both sexes (HH; n = 684) for Brahman cattle

born from 1984 to 1994 at the Subtropical Agricultural Research Station, Brooksville, Florida.

Age at puberty was defined as the age (days) at first detected ovulatory estrus. Measurements

of SC and HH were taken at 18 mo of age. Fixed effects considered in the SC model were

year of birth (YOB), age of dam (AOD), and age at measurement (AGE) as a linear covariate.

Fixed effects fitted to the AP model were YOB and AOD. Fixed effects in the HH model

were YOB, sex, AOD, and AGE as a linear covariate. Variances and covariances were

estimated using REML with a derivative-free algorithm and fitting a multiple trait animal model.

Estimates of heritability for SC, AP, and HH were .28, .42, and .65, respectively.

Estimates of genetic correlations between SC and AP, SC and HH, and AP and HH were

-.32, .19, and .25, respectively. Estimates of environmental correlations were .19 between SC

and HH, and -. 13 between AP and HH.

Estimates of genetic parameters indicate a favorable genetic relationship between SC in

Brahman bulls and AP in Brahman heifers under subtropical conditions. There was also

evidence that selecting Brahman bulls for HH would not adversely affect SC but would have

some detrimental effect on AP in female progeny.















CHAPTER 4
INFLUENCE OF FRAME SIZE AND BODY CONDITION ON PERFORMANCE IN
BRAHMAN CATTLE


Introduction


The effect of frame size (FS) on the cow's reproductive traits has become of greater

concern in recent years due to the preference for increased size, and particularly height, in

Brahman cattle as well as in nearly all other breeds. Frame size is defined by hip height at a

particular age and is correlated with growth rate. Thus, even though selection for increased FS

likely has been advantageous due to increased growth rate, its impact on female fertility traits

such as age at puberty and rebreeding efficiency while lactating may have been negative.

The influence of cow size on reproduction and maternal performance has been studied

primarily in composite or crossbred populations (Buttram and Willham, 1989) in which it was

difficult to determine whether differences were attributable to differences in size or to breed

composition. The magnitude of differences in cow size that exists in many breeds of beef cattle

in the United States today is great (Jenkins et al., 1991), and the within-breed studies that have

been reported to date have not examined the impact of such large differences on reproductive

and production traits.

Body condition score (BCS) has been shown to have an extremely important impact on

fertility rates in beef cattle in Florida (Kunkle et al., 1994) and, therefore, should be considered

56









57

in conjunction with the effects of FS. The objectives for this study were to determine the effect

of heifer FS and fall body condition score on age at puberty and subsequent calving rate,

calving date, calf survival rate, weaning rate, calf birth and weaning weights, preweaning ADG,

and kilograms of calf per cow exposed in first-, second- and third or greater-parity Brahman

dams.


Materials and Methods


Data Description and Animal Management

The data were collected from Brahman cattle born between 1984 and 1994 at the

Subtropical Agricultural Research Station (STARS), Brooksville, Florida. The geographical

coordinates of STARS (Main Station) are 280 37' 00" north latitude and 820 21' 30" west

longitude. Average annual rainfall is 1,372 mm, and over half of that falls in June, July, August,

and September. Average year-round temperature is approximately 220C, with occasional

frosts from November through March.

The foundation Brahman herd at STARS used to generate the females for this study

was composed of 54 purebred and 61 upgraded cows in 1983. The upgraded cattle

descended from Brahman-sired cows purchased from a commercial Florida herd using a

rotational crossbreeding program and were at least two-thirds Brahman. The grade cattle used

in this study had been upgraded using purebred sires for at least two additional generations.

The foundation cow herd was assigned to mating groups based on fall hip height measurements.

The mean hip height of the foundation mature cows was 136 cm and ranged from 128 to 145











cm. Two breeding herds of small FS sires mated to cows with the smallest hip heights

(generally under 135 cm), one breeding herd using a moderate FS sire with cows with

intermediate hip heights (generally 135 to 137 cm), and two breeding herds of large FS sires

with cows with the highest hip heights (generally over 137 cm) were used each year in an effort

to generate as much variation in hip height as possible in their resulting progeny. All sires used

were purebreds and were obtained from cooperating purebred herds as well as from within the

STARS Brahman herd. All heifers born from these matings were retained and assigned to

small (116.0 to 125.5 cm), medium (126.0 to 133.5 cm), and large (134.0 to 145.5 cm) FS

groups based on their 18-mo hip height. Only data from heifers generated in the study were

included in the analyses. Other than during the breeding season, females of differing FS were

maintained in the same contemporary groups. Females with physical (e.g., udder, feet, and leg

problems) or reproductive unsoundness (e.g., not pregnant two consecutive years) or diseases

were culled. No cows were culled on the basis of productivity (e.g., weaning weight of calves).

There were no major differences in culling rates among the FS groups.

A 120-d breeding season was used throughout the study. Heifers were first exposed at

approximately 24 mo of age. Calves were born from late December to early April. Calves

remained with their dams on bahiagrass (Paspalum notatum Flugge) pastures until weaning in

September, when calves were grouped by sex and fed a commercially prepared, medicated

supplement (65% TDN, 14% CP, plus antibiotics) for approximately 1 mo. Heifers were fed

.91 to 2.27 kg/d of concentrate (depending on the year) and 1.81 kg/d molasses (1993 to

1995), and hay (bahiagrass, perennial peanut, or Alyce clover) was provided for ad libitum









59

intake during winter until spring of the following year when growth of bahiagrass pasture was

adequate to support the heifers. As heifers approached 2 yr of age, during their second winter,

they were given free access to bahiagrass hay and 1.81 kg/d of molasses.

Cows grazed bahiagrass (Paspalum notatum Flugge) or mixed bahiagrass-legume

pastures throughout the study. Bahiagrass hay (large round bales) was offered free choice from

first frost (about November 15) through approximately April 1, when spring grass became

available. Cows were supplemented three times each week at a rate equivalent to .9 kg,

cow1 d 1 of a commercially available 20% CP range cube supplement (< 5% crude fiber,

<4% total mineral ingredients, > 2% crude fat, > 4,545 USP units vitamin A/kg, > 2,272 USP

units vitamin D3/kg, and > 4.5 USP units vitamin E/kg) fed on the ground. Depending on

availability, perennial peanut (Arachis glabrata Benth.) hay (large round bales) was substituted

for the 20% CP range cubes at the rate of 2.3 to 2.7 kg of perennial peanut hay for .9 kg of

20% CP range cube supplement. Additionally, cow herds were supplemented with blackstrap

molasses fed in open troughs twice weekly at a rate equivalent to 1.9 kg cow 1 d 1. Until

1989, supplementation of the cow herd with molasses began with first frost (approximately

November 15), and supplementation with 20% CP range cubes began at the start of calving

(approximately January 1). After 1989, supplementation of the cow herd with range cubes

began at first frost, and molasses supplementation began at the start of calving. As with the

feeding of hay, range cube and molasses supplementation ceased when pasture growth

commenced (approximately April 1). A custom mineral mixture (25% to 32% salt, 15 to 18%











Ca, 5to 8% P, > .94% Fe, < .15% F, > .10% Cu, > .01% Co, and .0010 to .0015% Se)

was offered throughout the year in mineral boxes.

The BCS for all females were recorded in September of each year when pregnancy

testing and weaning of calves were performed. The fall BCS was originally assessed on a scale

ranging from 1 = emaciated to 17 = extremely fat. These scores were reassigned to conform

with the 1-to-9 system of body condition scoring (Richards et al., 1986) currently being used

by the beef industry. Corresponding values reassigned from the scale 1 to 17 to the scale 1 to

9 were as follows: 1 to 1; 2 to 2; 3 and 4 to 3; 5 to 4; 6 and 7 to 5; 8 to 6; 9, 10, and 11 to 7;

12, 13, and 14 to 8; and 15, 16, and 17 to 9. Calving status was determined from calving

records and coded in the data as a categorical trait (1 = calved, 0 = did not calve).

Reproductive traits examined were age at puberty in heifers (AP) and their subsequent

calving rate (CR), calving date (CD), calf survival rate (SR), and weaning rate (WR). Age at

puberty was defined to be the age (days) at first detected ovulatory estrus. Criteria for

determination of age at puberty were described previously (Senseman, 1989; Vargas et al.,

1998). Calving rate was the percentage of cows exposed during the breeding season that

subsequently calved. Calf survival was the percentage of calves born alive that survived to

weaning (1 = survived, 0 = died before weaning). Calving date was expressed as a Gregorian

date. Weaning rate was defined as the percentage of cows exposed to breeding that weaned a

calf (1 = weaned, 0 = did not wean). Production traits evaluated were actual birth weight

(BWT), actual weaning weight (WWT), preweaning ADG, and production per cow (PPC).









61

Production per cow was expressed as actual kilograms of calf weaned relative to the total

number of cows that entered the breeding season.

The reproductive and calf weight traits were analyzed separately for the three parity

groups of cows. The parity groups were first-parity dams, second-parity dams, and third or

greater-parity dams. Records considered for the last two parity groups were limited to those

for cows that weaned a calf the previous year to ensure that only cows lactating during the

breeding season were included in the analysis. Because cows were not culled unless they were

not pregnant for two consecutive years, cows that failed to become pregnant as lactating 3-yr-

olds could have reentered the data set as lactating 5-yr-olds while being rebred to calve at 6 yr.

Pregnancy data for nonlactating 4-yr-olds and the weight and other data from this subsequent

calf born at 5 yr were not included in the analyses. Therefore, the records used in any

subsequent parity were a subset of the records for the previous parity. Because this subset of

the data defines a subpopulation of females required to become pregnant while lactating, it

more closely represents a commercial population. Total number of dams meeting the above

criteria for each parity were as follows: first parity, 215; second parity, 130; and third or greater

parity, 267. Throughout the study, husbandry was in accordance with guidelines recommended

by the Consortium (1988).

Statistical Analysis

Age at puberty in heifers was analyzed using a least squares model that included the

fixed effects of year of birth (YR), FS, BCS, and the interaction effects. Data for hip height of

heifers at 18 mo of age were initially analyzed using a least squares model that included the









62

fixed effects of YR, FS, and the interaction effect. Because the interaction was not significant, it

was deleted from the original model, and the data were reanalyzed using the reduced model.

To evaluate the relationship between FS and BCS within each parity group, data were fitted by

least squares methods to a model that considered BCS as the dependent variable and YR and

FS as the independent variables. When the YR x FS interaction was not significant, it was

deleted from the original model, and the data were reanalyzed using the reduced model.

Main effects included in the final model used to evaluate the reproductive traits,

including AP in heifers, and production traits in first-, second-, and third or greater-parity dams

were YR, FS, BCS, FS x BCS interaction, and a random error component. Analyses for CD,

SR, BWT, and WWT considered the additional effect of sex of calf (SEX), which was

dropped from the original model when found not to be significant. In the analysis of CD of the

lactating cows, the effect of sex of the nursing calf was included. All possible two-factor

interactions involving this effect were included in preliminary analyses, but because they did not

influence (P > .15) any of the variables, they were removed from the original model, and the

data were reanalyzed using the reduced model. Parity differences in the third or greater-parity

group were partially confounded with year effects. Linear contrasts were computed for

comparison of levels of FS and BCS for each of the three parity groups of dams. Data were

analyzed by least squares ANOVA using the GLM procedure of SAS (1988) and are reported

as least squares means + SE.











Results and Discussion


Hip Height and Body Condition Score

Large FS heifers (136.4 .45 cm) were taller (P < .001) than medium FS (129.2 1

.23 cm) and small FS (121.7 .27 cm) heifers. The relationships between FS and BCS in

each of the three parity groups of cows are presented in Table 4- 1.


Table 4- 1. Least squares means SE for body condition scores (BCS) for first-,
second-, and third or greater-parity Brahman dams by frame size (FS)

Parity

n First n Second n Third or


Item greater

Mean 215 6.0 + .05 130 4.1 .07 267 4.7 .05
FS
Small 77 6.2 .08a 48 4.1 .12 107 4.7 .09
Medium 97 5.9 .07b 61 3.9 .11 101 4.5 .09
Large 41 5.61 .130 21 4.1 .19 59 4.5 .12
a,b,c Means with a different superscript letter within a column differ (P < .05).


Effects of YR and FS on BCS of first-parity dams were important (P < .001). Even

though this parity group represents nonlactating 212-yr-old heifers, the FS effects on BCS show

that large FS heifers achieved lower (P < .05) BCS than the small and medium FS heifers. The

lower BCS for the large FS heifers indicate that the nutritional level in this experiment did not

adequately meet their requirements.











Frame size was not an important source of variation for BCS in second-parity (P =

.43) or third or greater-parity (P = .17) dams, probably because lactational energy demands

obscured any direct effect of size, especially as the cows reached maturity. Body condition

score in lactating cows seemed to remain almost constant (> 4.5) in subsequent parities.




Table 4-2. Least squares means SE for age at puberty (AP) by
frame size (FS) and body condition score (BCS) at 18 mo of age in
Brahman heifers

Item n Age at puberty, d

FS

Small 75 633 12.3a

Medium 84 626 12.0a

Large 34 672 17.1b

BCS

3 50 666 + 13.8

4 48 653 14.6

5 58 631 + 13.3

6 16 628 + 24.9

7 21 640 21.2
a,b Means with different superscripts within a column and item (i.e., FS
and BCS) differ (P < .05).




Age at Puberty

The average age at puberty in heifers was 633 6.7 d. In the southern United States,

AP of 816 d (Reynolds et al., 1963), 537 d (Baker et al., 1989), and 590 d (Plasse et al.,









65

1968) have been reported for Brahman heifers, whereas in Argentina, Mezzadra et al. (1993)

reported AP of 507 d.

In general, Bos indicus heifers achieved puberty at later ages than Bos taurus heifers

(Plasse et al., 1968; Galina and Arthur, 1989). In a five-breed diallel that included the Angus,

Brahman, Hereford, Holstein, and Jersey breeds and their crosses, Nelsen et al. (1982)

reported that straightbred Brahman heifers were the oldest, heaviest, and tallest at puberty.

Frame size tended to be a significant source of variation (P = .06) for AP (Table 4-2). Small

(633 12.3 d) and medium (626 12.0 d) FS heifers were younger (P < .05) at puberty than

large (672 17.1 d) FS heifers. Body condition score (P = .29) and the interaction FS x BCS

(P = .35) did not affect AP. For Bos taurus breeds, Ferrell (1982) reported that AP was not

related to BCS of heifers at 452 d of age. Furthermore, Grass et al. (1982) failed to

demonstrate that heifers attained puberty at a consistent level of body condition.

Calving Rate

Calving rate in first-parity dams averaged 92.1 + 1.76% in this study. A similar value

(90%) was reported by Peacock and Koger (1980) for Brahman heifers from several ranches

in Florida. Frame size did not influence (P < .31) CR in first-parity heifers. Because heifers

were exposed to breeding at 2 yr of age when the majority of them had already reached

puberty, FS was not expected to influence CR (Morris, 1980).

Frame size group had a significant effect (P < .05) on the CR of second-parity dams.

Only 63.1 3.21% of the young Brahman females that weaned their first calf calved the

subsequent year. Calving rate in large FS second-parity dams (41.0 + 8.38%) was more than









66

25% lower than that in small (65.8 5.42%) and medium (69.0 4.85%) FS cows (Table

4-3).


Table 4-3. Least squares means SE for calving rate (CR) by frame size (FS) and body
condition score (BCS) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-
parity dams

Item n CR, % n CR, % n CR, %


FS

Small 77 93.5 + 3.09 48 65.8 5.42a 107 93.5 + 3.410

Medium 97 88.5 + 2.71 61 69.0 + 4.85a 101 78.5 + 4.02d'

Large 41 97.3 + 6.81 21 41.0 + 8.38b 59 79.8 5.33d

BCS

3 0 44 17.1 6.540 22 67.5 6.100

4 0 41 69.4 + 6.72d 79 86.7 + 3.26d

5 68 84.5 + 3.40a 45 88.8 6.44e 141 94.5 + 2.58e

6 86 96.6 + 3.23b 0 25 87.1 + 6.81d

7 61 98.3 6.75b 0 0 -

a,b Means with a different superscript letter within a column and item (i.e., FS and BCS)
differ (P < .05).
c,d,e Means with a different superscript letter within a column and item differ (P < .01).


The number of observations for large FS second-parity females is low because the low

survival rate of calves from first-parity large FS females resulted in their dams being eliminated

from the second-parity analysis. Calving rate in mature dams (third or greater-parity dams)









67

averaged 90.3 1.63% and was affected (P < .01) by FS. The CR of mature small FS cows

was greater (P < .01) than that of the medium and large FS mature cows.

Calving rate improved with increasing BCS. Calving rate in first-parity dams with BCS

5 was lower (P < .05) than that of dams having BCS 6 or 7. Calving rate of second-parity

dams with BCS 3 was markedly lower (P < .01) than that of cows with BCS 4 or 5. In mature

dams, CR was the lowest (P < .01) in cows with BCS 3. Mature cows with BCS 4 or 6 had

comparable CR values. These results are in accord with previous studies of Bos taurus and

Bos indicus beef cattle in which body condition score corresponded directly to pregnancy and

calving rates (Richards et al., 1986; Kunkle, 1994; Vargas, 1994).

No FS x BCS interaction was detected in first- and second-parity dams for CR. Thus,

within each FS group, CR was favorably and directly related to BCS. However, in third or

greater-parity dams there was a FS x BCS interaction (P < .01). Within BCS 3, the calving

rate of large FS cows was greater (P < .05) than the CR of medium FS cows. Within BCS 4,

the CR of large FS cows was greater (P < .05) than the CR of both the small and medium FS

cows. Within the moderate BCS groups (BCS 5 and 6), taller cows had a lower CR than

those of small and medium FS mature cows.

Calving Date

Cows that calve late in the calving season often do not return to estrus before the end of

the subsequent breeding season. Thus, CD is an important reproductive trait. Overall CD for

first-parity dams averaged 34.6 1.78 d and was similar among the three FS (Table 4-4).









68

Second-parity dams (CD = 62.6 3.37 d) calved later in the calving season, indicating

that conception occurred approximately 30 d later than that of the nonlactating 2-yr-olds in the

first-parity group. Growing young cows that are under lactational stress likely suppress cyclic

ovarian activity and as a result have a prolonged period of postpartum anestrus (Williams,

1990). Short et al. (1990) reported that first-calf heifers (2 yr old) had longer postpartum

intervals of anestrus and lower reproductive rates than dams 3 yr old and older. There was a

tendency for the taller cows to calve later than shorter cows.


Table 4-4. Least squares means SE for calving date (CD)
condition score (BCS) for parity groups of Brahman cattle


by frame size (FS) and body


First-parity dams Second-parity dams Third or greater-parity
dams

Item n CD, d n CD, d n CD, d

FS

Small 72 33.9 + 3.14 34 55.0 + 8.49 100 59.3 + 3.80

Medium 87 33.8 + 2.83 38 65.0 + 5.65 87 65.0 + 5.30

Large 39 36.9 + 6.61 10 82.0 + 13.70 53 64.0 7.08

BCS

3 0 9 67.1 + 14.00 15 87.4 + 8.58a

4 0 32 77.3 + 7.55 69 60.4 3.79b

5 55 50.0 + 3.54a 41 57.5 + 6.13 132 56.2 + 2.91b

6 84 28.8 3.16b 0 24 47.0 + 8.50b

7 59 25.8 + 6.55b 0 0-
a,b Means with a different superscript letter within a column and item (i.e., FS and BCS)
differ (P < .05).











There were no differences among the FS for CD in mature cows, nor was the

interaction FS x BCS significant. Overall, small and medium FS cows with similar and

adequate BCS (> 5) became pregnant earlier than large FS cows and, as a result, they are

more likely to calve successively over a number of years.

Body condition score the previous fall influenced (P < .01) CD. Heifers with greater

BCS at 18 mo calved earlier (P < .05) than heifers with lesser BCS. Body condition score the

previous fall did not affect (P =. 15) CD in second-parity dams. Although the number of

pregnancies was affected by BCS, BCS did not seem to be a determining factor of when the

pregnancies occurred. Overall CD for lactating mature cows was 55.5 1.87 d and was

affected (P < .01) by BCS. Cows with BCS 3 calved later (P < .05) than cows with higher

BCS.

Survival Rate

Calf survival rate was affected by FS (P < .05) only in first-parity dams. Survival rate

was greater (P < .01) for calves out of small (80.7 5.23%) and medium (83.4 4.71%) FS

first-calf heifers bred to comparably sized bulls than for calves out of large FS first-calf heifers

bred to large FS sires (47.9 11.00%; Table 4-5).

There is no reason to expect calves from the large FS first-parity dams to be more

susceptible to cold weather or "weak calf syndrome" (Franke et al. 1975; Turner, 1980). It

seems likely that a greater incidence of calving difficulty associated with their larger calves

(Bellows and Short, 1994) is primarily responsible for their very low survival rate Survival









70

rates in calves out of second-parity and mature dams were not affected (P < .14) by FS or

BCS.


Table 4-5. Least squares means SE for survival rate (SR) by frame size (FS) and body
condition score (BCS) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n SR, % n SR, % n SR, %

FS

Small 72 80.7 + 5.23a 34 97.5 6.44 100 77.6 4.76

Medium 87 83.4 + 4.71a 38 88.1 + 4.27 87 86.9 6.62

Large 39 47.9 11.00b 10 93.9 10.33 53 95.7 8.87

BCS

3 0 9 95.3 10.57 15 88.8 10.76

4 0 32 92.8 5.68 69 94.1 4.74

5 55 82.2 5.89 41 91.4 4.50 132 85.5 3.65

6 84 73.3 5.25 0 24 78.5 10.60

7 59 56.5 10.89 0 0 -

a,b Means with a different superscript letter within a column and item (i.e., FS and BCS)
differ (P < .01).


Weaning Rate

Frame size affected (P < .05) WR in first- and second-parity dams. Small and medium

FS had greater (P < .05) weaning rates than the large FS heifers and cows (Table 4-6). The

lower WR for the large FS first-parity cows in this study was primarily due to increased calf









71

mortality because these heifers were bred to the large FS sires. The extremely low pregnancy

rate seems to have been responsible for the reduced WR in the second-parity group. Frame

size was not a factor influencing WR in third or greater-parity cows.


Table 4-6. Least squares means SE for weaning rate (WR) by frame size (FS) and
body condition score (BCS) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n WR, % n WR, % n WR, %


FS

Small 77 75.0 + 5.33a 48 64.9 + 5.81a 107 71.8 + 5.33

Medium 97 74.3 4.67a 61 59.8 5.20a 101 68.5 6.28

Large 41 46.2 + 11.76b 21 38.3 8.98b 59 75.8 8.33

BCS

3 0 44 17.9 + 7.00a 22 58.8 9.53

4 0 41 64.6 7.20b 79 82.1 5.09b

5 68 69.8 + 5.88 45 80.6 6.90b 141 80.5 4.03b

6 86 70.8 + 5.58 0 25 66.4 + 10.63a

7 61 54.8 11.65 0 0 -

a,b Means with a different superscript letter within a column and item (i.e., FS and BCS)
differ (P < .05).











Fall body condition score did not affect WR in first-parity dams. Weaning rate in

second-parity dams with BCS 3 was lower (P < .05) than those of dams with BCS 4 or 5.

Weaning rate of third or greater-parity dams tended to be affected (P < 10) by BCS.

Weaning rate in mature dams with BCS 3 was 58.8 9.53%, lower (P < .05) than that

observed in dams with BCS 4 (82.1 5.09%) and BCS 5 (80.9 4.03%), but, unexpectedly,

similar to the WR (66.4 10.63%) observed in dams with BCS 6.

Birth Weight

The average BWT of calves born in this study was 32.3 + .39 kg. Reynolds et al.

(1980) reported a 25.8-kg birth weight for Brahman calves. In his review, Plasse (1978)

reported an average unadjusted birth weight in Brahman calves in Latin America of 27.2 kg

and an average of 28.4 kg for the United States. Male calves were heavier (P < .05) at birth

than female calves out of all parity groups of dams (Table 4-7), in agreement with results

observed in previous studies (Plasse, 1978; Thrift, 1997).

Frame size had an effect (P < .01) on BWT of calves out of all three dam parity

groups. Within first-parity dams, BWT of calves increased (P < .05) with FS. A similar

tendency was observed in the second- and third or greater-parity dams group. The average

BWT of calves from the large FS cows was approximately 8 kg greater than BWT of calves

from the small FS cows across all parity groups. This difference is due in part to the differential

in FS of the bulls used. If all FS groups of females had been mated to similarly sized bulls, we

would expect smaller differences in BWT among the FS groups.









73

These results are supported by those of Jenkins et al. (1991), who found a positive

within-breed phenotypic correlation (.37) between BWT and adult hip height. Even though

Gore et al. (1994) did not find a relationship between BWT and maternal size, large cows

tended to have calves of greater BWT than cows of smaller size.


Table 4-7. Least squares means SE for birth weight (BWT) by frame size (FS), body
condition score (BCS), and sex of calf (SEX) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n BWT, kg n BWT, kg n BWT, kg

SEX

Male 107 33.2 + .65a 43 35.8 .91a 117 35.3 .67a

Female 91 30.5 .73b 39 32.3 1.07b 123 32.9 .67b

FS

Small 72 28.0 + .68a 34 30.1 + 1.20a 100 29.9 .66a

Medium 87 31.4 + .61b 38 34.2 .80b 87 33.9 + .91b

Large 39 36.0 + 1.430 10 37.8 + 1.97b 53 38.6 + 1.250

BCS

3 0 9 31.8 1.97 15 35.1 + 1.43

4 0 32 35.3 1.05 69 35.1 .65

5 55 33.1 + .76a 41 35.0 + .86 132 33.9 + .54

6 84 30.5 .68b 0 24 32.5 1.47

7 59 31.9 1.42b 0 0 -

a,b,c Means with a different superscript letter within a column and item (i.e., SEX, FS, and
BCS) differ (P < .05).









74

Body condition score tended (P < 10) to affect BWT in first-parity dams. However,

heifers with BCS 5, the lowest score within this parity group, had calves with greater (P < .05)

BWT (33.1 + .76 kg) than heifers with BCS 6 (30.5 + .68 kg) or BCS 7 (31.9 1.42 kg), a

trend that is not readily understood. Body condition score of cow did not affect BWT of calves

from second- (P = .27), and third or greater-parity (P = .23) dams. However, absolute values

for mature cows (Table 4-7) show a tendency for the birth weights of their calves to decrease

with increased BCS.

Weaning Weight

The WWT of the calves were similar across parity groups. Calves from the first-parity

dams were older at weaning, and this overcame the anticipated lower WWT. Sex of calf

influenced WWT of calves out of first- (P < .001) and second-parity (P < .05) dams but not

out of the third or greater-parity dam group (P = .53).

Frame size affected (P < .001) WWT of calves from first-parity dams. Weaning

weights of calves from small FS cows (192.7 4.40 kg) were lower (P < .05) than those of

calves out of medium (216.3 3.92 kg) and large (226.0 7.01 kg) FS cows. Frame size did

not affect (P = .98) WWT of calves out of second-parity dams. In the third or greater-parity

group, small and medium FS dams weaned calves of similar weights (199.2 6.95 and 203.3

8.53 kg, respectively), both of which were lighter (P < .05) than those weaned by large FS

dams (231.2 10.79 kg). The expected superiority of the large FS dams for WWT, which

was not expressed in second-parity dams, was probably due to the later calving dates for this

FS group.











Table 4- 8. Least squares means SE for weaning weight (WWT) by frame size (FS),
body condition score (BCS), and sex of calf (SEX) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n WWT, kg n WWT, kg n WWT, kg

SEX

Male 79 218.9 3.99a 40 201.6 + 7.640 94 213.2 + 6.35

Female 74 204.4 4.12b 37 183.2 8.80d 111 209.3 6.16

FS

Small 55 192.7 + 4.400 34 191.4 + 9.69 80 199.2 + 6.95e

Medium 72 216.3 3.92d' 33 191.8 + 6.92 77 203.3 8.530

Large 26 226.0 7.01d' 10 193.9 + 15.99 48 231.2 10.79d

BCS

3 0 9 182.8 15.93 12 190.5 13.46

4 0 30 194.1 + 8.61 63 217.4 + 5.90

5 45 201.6 5.120 38 200.2 7.12 113 212.2 5.05

6 64 216.0 4.63d 0 17 224.8 12.92

7 44 217.4 6.00d 0 0 -

a,b Means with a different superscript letter within a column and item (i.e., SEX, FS, and
BCS) differ (P < .001).
c,d Means with a different superscript letter within a column and item differ (P < .05).




Body condition tended (P = .09) to affect WWT in first-parity dams. Thus, heifers that

entered the previous winter season in better body condition tended to wean heavier calves the

next fall. Part of this weight advantage for calves from heifers in better BCS is also likely due to

their earlier CD (Table 4-4) that allowed their calves to be older, and thus, heavier, at









76

weaning. In older dams, as BCS increased, WWT of their calves increased numerically (Table

4- 8). This may reflect the ability of older cows to maintain more fat reserves that could be

mobilized for milk production.

Preweaning Average Daily Gain

Average daily weight gains of the nursing calves are presented in Table 4-9. Sex of

calf influenced ADG of calves out of first- (P < .001) and second-parity (P < .05) dams but

not that of calves from third or greater-parity dams (P = .22).

Frame size affected (P < .05) ADG of calves. Preweaning ADG of calves from small

FS first-parity cows (747 15.96 g/d) was lower (P < .01) than that of calves from medium

(837 14.21 g/d) and large FS cows (900 25.42 g/d). In second- and third or greater-

parity dams, calves out of large FS cows were the fastest-gaining (P < .05) compared to those

out of small and medium FS cows. These differences, which are consistent with the other

growth traits evaluated, likely reflect a positive phenotypic correlation between milk production

and body size of the cow (Morris and Wilton, 1976), the inherent growth pattern of the large

frame size calf (Menchaca et al., 1996), and the ability of the fastest-gaining calves to consume

enough forage to meet their increased nutritional demands for growth (Grings et al., 1996). No

difference was found in ADG of calves from first-, second-, and third or greater-parity dams

attributable to the effect of body condition score.









77

Table 4-9. Least squares means SE for preweaning average daily gain (ADG) by frame
size (FS), body condition score (BCS), and sex of calf (SEX) for parity groups of Brahman
cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n ADG, g/d n ADG, g/d n ADG, g/d

SEX

Male 79 864 14.45a 40 891 25.940 94 897 23.69

Female 74 792 14.92b 37 812 28.95d 111 868 22.97

FS

Small 55 747 15.960 34 815 26.180 80 831 25.920

Medium 72 837 14.21d 33 817 24.130 77 858 31.840

Large 26 900 25.42d 10 922 47.27d 48 958 40.26d

BCS

3 0 9 853 47.01 12 864 50.22

4 0 30 882 27.80 63 908 22.02

5 45 819+ 18.33 38 819 24.70 113 884+ 18.82

6 64 828 + 16.80 0 17 872 48.20

7 44 837 21.76 0 0 -
a,b Means with a different superscript letter within a column and item (i.e., SEX, FS, and
BCS) differ (P < .001).
c,d Means with a different superscript letter within a column and item differ (P < .05).




Production Per Cow

Weight of calf weaned per cow exposed is more important than calf weaning weight

per se (Ferrell, 1982) and is a function of calving rate, calf survival rate, and calf weaning









78

weight. Overall production per cow (PPC) averaged 148.4 6.65, 113.1 7.02, and 161.7

5.79 kg of calf for first-, second-, and third or greater-parity dams, respectively.


Table 4- 10. Least squares means SE for production per cow (PPC) by frame size (FS)
and body condition score (BCS) for parity groups of Brahman cattle

First-parity dams Second-parity dams Third or greater-parity
dams

Item n PPC, kg n PPC, kg n PPC, kg

FS

Small 77 143.3 11.64a 48 121.8 11.85a 107 140.6 12.30

Medium 97 161.9+ 10.21a 61 115.4+ 10.60a 101 150.3 14.30

Large 41 102.9 25.70b 21 80.5 + 18.31b 59 176.8 + 19.84

BCS

3 0 44 32.1 + 14.29a 22 107.2 21.49a

4 0 41 123.1 + 14.68b 79 179.4 11.71b

5 68 140.2 + 12.84 45 162.6 + 14.080 141 172.4 + 9.92b

6 86 153.6 + 12.19 0 25 164.7 24.52b

7 61 114.4 25.46 0 0 -

a,b,c Means with a different superscript letter within a column and item (i.e., FS and BCS)
differ (P < .05).


The kilograms of calf weaned per cow exposed tended (P = .08) to be influenced by

FS in first-parity dams (Table 4- 10). Production per cow of small (143.3 11.64 kg) and

medium (161.9 10.21 kg) FS first-parity dams were similar and both tended (P = .07) to be

greater than the PPC of large FS cows (102.9 25.70 kg). In second-parity dams, the PPC









79

differences for the large FS cows compared to the small and medium FS cows were not as

great (P = .16). Similarly, the effect of FS on production per cow in third or greater-parity

dams was not significant (P = .28), but, contrary to the results seen for younger cows, mature

cows of large FS produced more calf weight at weaning per cow exposed to breeding than

either medium or small FS mature cows. The calves from large FS cows were, however, sired

by larger FS bulls than those from the small and medium FS groups.

The kilograms of calf weaned per cow exposed in first-parity dams was not affected (P

= .35) by BCS. In second-parity dams, however, PPC was highly affected by BCS (P <

.001). In third or greater-parity dams, production per cow was affected (P < .05) by BCS,

and there was a tendency (P = .10) for the FS x BCS interaction to affect it as well. Second-

parity dams with BCS 3, 4, and 5 weaned 32.1 + 14.29, 123.1 + 14.68, and 162.6 14.08

kg of calf per cow, respectively. Mature cows with BCS 3, 4, 5, and 6 weaned 107.2 +

21.49, 179.4 11.71, 172.4 9.92, and 164.7 24.52 kg of calf, respectively.

These results indicate that variation in cow FS affects reproductive and production

performance in Brahman cattle and that the impact of FS on reproductive performance was

greater at younger ages (first- and second-parity dams) than in mature dams (third or greater-

parity dams). As the large FS Brahman cows matured, they seemed to have overcome the

negative effects imposed by FS that were observed at younger ages. Their pregnancy rates,

calf survival rates, and body condition scores were generally all comparable to those of smaller

cows once they had reached maturity. Thus, after the large FS cows ceased growing, the

nutritional regimen provided at STARS seemed to more closely meet their requirements for









80

maintenance and lactation. The small FS cows were able to meet their nutrient requirements

during lactation and, thus, maintained adequate body condition scores and higher pregnancy

rates as young cows. Likely, this is also a reflection of earlier maturity in the small FS group

(Menchaca et al., 1996).


Implications


The practice of selecting Brahman cattle for greater hip heights seems likely to have

resulted in delayed puberty and reduced female fertility in young lactating females. It may be

possible to overcome some of these disadvantages through increased nutrition, but the costs

associated with this added nutrition may be excessive, especially in purebreds with excessive

frame scores. Although cattle with the shortest hip heights may have better fertility traits, their

reduced growth potential and the possibility of inadequate carcass weight must also be

considered in determining the optimal cow size for a given management situation. The

recommended cow size is likely to be a moderate one so that the cows can be maintained in

adequate body condition under nutritional levels attainable under commercial conditions and

produce steer progeny with acceptable carcass weights.


Summary


The effects of frame size (FS) and body condition score (BCS) on performance of

Brahman cows were evaluated using records collected from 1984 to 1994 at the Subtropical

Agricultural Research Station, Brooksville, Florida. Age at puberty (AP), calving rate (CR),









81

calving date (CD), survival rate (SR), weaning rate (WR), birth weight (BWT), weaning weight

(WWT), preweaning ADG, and kilograms of calf produced per cow exposed (PPC) were

obtained from first- (n = 215), second- (n = 130), and third or greater-parity (n = 267) dams.

Based on hip height at 18 mo of age, heifers were assigned to three FS groups: small (115 to

126 cm), medium (127 to 133 cm), or large (134 to 145 cm).

Small and medium FS heifers attained puberty at younger (P < .05) ages (633.2 +

12.3 and 626.4 12.0 d) than large FS heifers (672.3 17.1 d). Calving rate in large FS

second-parity dams was 27% less (P < .05) than in small and medium FS dams. In third or

greater-parity dams, CR was greater (P < .05) for small FS cows than for medium and large

FS cows. Across the three parity groups, CR improved with increasing BCS. Except for the

first-parity dams, animals with better fall BCS calved earlier (P < .05). In first-parity dams, SR

was less (P < .01) in large (47.9 11.0%) than in small (80.7 5.2%) and medium (83.4

4.7%) FS groups. Weaning rates of large FS first- and second-parity dams were less (P <

.05) than those of small and medium FS dams. Second-parity dams with BCS 3 had lower (P

< .05) WR than dams with BCS 4 and 5. Within first- and third or greater-parity dams, BWT

of calves born to small FS cows were the lightest, and those born to large FS dams were the

heaviest; those born to medium FS dams were intermediate (P < .05). In second-parity dams,

BWT of calves of large FS dams were greater (P < .05) than those of small and medium FS

dams. In first-parity dams, calves weaned by small FS cows had lower (P < .05) WWT than

those weaned by higher FS cows. In the third or greater-parity group, large FS dams weaned

heavier calves (P < .05) than other dams. In all parity groups of dams, calves out of large FS









82

cows had greater ADG (P < .05) than those from small and medium FS cows. In first-parity

dams, PPC was comparable between small and medium FS dams, but both tended to be

greater (P < 10) than PPC of large FS dams.

Small and medium FS females reached puberty at an earlier age, calved earlier, and

had greater calving, survival, and weaning rates, as well as greater kilograms of calf produced

per cow exposed than the large FS females. As the large FS cows matured, they seemed to

have overcome the negative effects imposed by FS that were observed at younger ages. Their

performance traits were generally all comparable to those of smaller cows once they had

reached maturity.















CHAPTER 5
GENETIC PARAMETERS AND RELATIONSHIPS BETWEEN HIP HEIGHT AND
WEIGHT IN BRAHMAN CATTLE


Introduction


Breeders have used over the years body size characteristics to implement strategies for

the genetic improvement of beef cattle (Jenkins et al., 1991). Body size recommendations have

usually been based on weight and(or) weight gains (Jenkins et al., 1991; Hoffman, 1997).

Another trait that has been used to change body size is hip height. Hip height is directly related

to body size and has been found to be negatively associated with productivity of beef females

(Buttram and Willham, 1989; Vargas et al., 1999). Results of a favorable genetic relationship

of hip height with scrotal circumference and unfavorable genetic relationship with age at puberty

of heifers have been reported (Brinks, 1994; Vargas et al., 1998). However, neither weight

nor hip height alone can account for all genetic differences in body size exhibited by beef (BIF,

1996) or dairy cattle (Hoffman, 1997). Perhaps a multiple trait evaluation including both hip

height and weight is a better option for selection for body size. The genetic evaluation of hip

height at various ages and its relationships with weaning weight should improve the genetic

evaluation for size and may also aid in the selection for reproductive traits.









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Selection decisions for replacement breeding animals may be made at 12 to 18 mo of

age. Early and accurate prediction of performance at later ages is of substantial economic

value. For early selection decisions to be effective, reliable estimates of genetic parameters for

associated traits measured at young and older ages and their genetic relationships are needed.

Furthermore, the nature of the relationship between estimated breeding values for one trait

measured early (e.g., weaning) and another trait measured at a later age (e.g., 18 mo of age)

would facilitate the decision making process.

Thus, the objectives of this study were: 1) to estimate the direct genetic and maternal

genetic effects for hip height and weight at weaning, postweaning hip height growth, and hip

height at 18 mo of age; 2) to estimate genetic correlations between weaning hip height and

weaning weight, and between weaning hip height and postweaning hip height growth, and

between weaning weight and hip height at 18 mo of age; and 3) to examine the possibility of

using estimated breeding values for height or weight at weaning to predict performance for hip

height at 18 mo of age in Brahman cattle.


Materials and Methods


Data Description

Data were collected from Brahman cattle born between 1984 and 1994 at the

Subtropical Agricultural Research Station (STARS) located near Brooksville, Florida. The

Brahman herd at STARS used in this study was composed of purebred and upgraded cattle.

The grade cattle descended from Brahman-sired cows, with at least two-thirds Brahman











breeding, upgraded for two or three additional generations. Complete pedigree records

relating all animals to the base herd were available. The number of sires used per year ranged

from two to five. To maintain connectedness of the data across years, up to three sires were

used in two consecutive years. Assortative mating based on observed hip height was practiced,

mating groups were formed such that dams and sires were of comparable frame score. The

total number of sires and dams that had offspring with records was 28 and 261, respectively.

The number of records per trait was 889 weaning hip heights, 892 weaning weights, and 684

hip heights at 18 mo of age. Hip heights were measured according to the Beef Improvement

Federation guidelines (BIF, 1996). Postweaning hip height growth (PHG) was calculated by

multiplying postweaning average daily hip height growth by 345. Postweaning average daily

growth was calculated based on 205-d and 550-d hip height adjusted in accordance with the

BIF (1996) recommendations. Details of the management of calves, bulls, and heifers are

described by Vargas et al. (1998; 1999).

Statistical Analysis

The matrix of additive genetic relationship was complete for all animals evaluated in this

study. Thus, changes in (co)variances that might have occurred as a result of the assortative

mating would not affect the relationship matrix (Sorensen and Kennedy, 1984; Fernando and

Gianola, 1990; Henderson, 1990). Data were analyzed using an animal model (Henderson and

Quaas, 1976; Quaas and Pollak, 1980). Additive direct and maternal effects were taken into

account by including appropriate random effects into the model's analysis. However, due to

the small size of the data set that did not allow convergence when three or more traits were











included in the multiple trait model. Therefore, only bivariate analyses were conducted.

Weaning hip height (WHH), weaning weight (WWT), hip height at 18 mo of age (HH18), and

PHG were the traits considered. Number of observations, phenotypic means, standard

deviations, minimums, and maximums for the traits studied are presented in Table 5- 1. No

adjustment of any trait was made before analyses.



Table 5- 1. Number of observations (n), means, standard
deviations (SD), minimums, and maximums for hip height (WHH;
cm) and weight (WWT; kg) at weaning, postweaning hip height
growth (PHG; cm), and hip height at 18 mo of age (HH18; cm) in
Brahman cattle

Traits n Mean SD Min. Max.

WHH 889 113.19 6.46 89.00 136.00

WWT 892 216.48 36.59 135.20 327.00

PHG 684 19.90 8.37 4.00 46.60
HH18 684 132.39 8.24 109.50 159.50




Fixed effects considered in the model were year, sex of calf, and age of dam for all

models, and age of calf at weaning as a linear and quadratic covariate for the weaning traits,

and age at measurement as a linear and quadratic covariate for HH18. Random effects were

direct of the animal, maternal of the dam, and residual. Animal and dam effects were

connected through the additive relationship matrix, and the matrix of genetic covariances

between traits. The full relationship matrix between animals was included by incorporating all









87

pedigree information. The two-trait animal model (Appendix B) followed that of Quaas and

Pollak (1980).

Thus, the (co)variance parameters to be estimated in each bivariate analysis were two

additive genetic variance components (OAll and A22 ), the additive genetic covariance

component between them (O A,2 ), two maternal genetic variance components (OM1 and

am22 ), the genetic covariance component between them (a ), four genetic covariance

components between direct and maternal effects (O AM a 22 U 7A1M2 and A2M1 ), and

three residual error (co)variances ( e,11 22 and U'12 ). Three two-trait analyses were

conducted. Analyses considered pairing the traits WHH-WWT, WHH-PHG, and WWT-

HH18. These pairings were chosen because it was assumed firstly that WWT-PHG was

adequately explained by WWT-HH18, and secondly that since WHH and PHG were each

constituent parts of HH18, the expected collinearity effect may be affecting convergence in the

solutions when pairing the traits WHH-HH18 and PHG-HH18. Genetic parameters were

estimated for WHH, WWT, HH18, and PHG. Heritability estimates for each trait and the

genetic and environmental correlations between direct and maternal effects within each two-trait

analysis were also computed.

Analyses were carried out using multiple trait derivative-free restricted maximum

likelihood (MTDFREML) programs (Boldman et al., 1995). The strategy for the estimation of

the (co)variances was as follows: 1) starting values for the direct additive genetic variance,

maternal additive genetic variance, and covariance between direct and maternal effects were

estimated in single-trait analyses; 2) two-trait analyses were initiated holding the (co)variance









88

estimates from single trait analyses constant until the variance of the value of the simplex

function was less than 10 3; 3) analyses were continued using the apparently converged

estimates from step 2 as starting values and re-estimating simultaneously all parameters in the

model using the same low level of convergence as in step 2; 4) analyses were repeated as in

step 3 until -2 log likelihood did not change in the first two decimal positions; 5) all parameters

in the model were simultaneously re-estimated using as initial values the estimates values

obtained in step 4 until the variance of the value of the simplex function was less than 10 9; and

6) to assured convergence to a global maximum, repeated analyses similar to step 5 were

conducted until the smallest -2 log likelihood was found. Changes in -2 log likelihood beyond

the third decimal position were considered not important.

Estimates of breeding values (EBV) were obtained for each trait within each bivariate

model, and used to determine the ranking of animals within the herd. Pearson product-moment

correlations between EBV and Spearman correlations between ranks of animals were

calculated for each trait using estimates from each bivariate model.


Results and Discussion


Productive and reproductive characteristics in Brahman cattle seem to be related to hip

height (Vargas et al., 1998; 1999). Knowledge of the genetic relationship between hip height

and weight at weaning, together with the understanding of the strength of the genetic relationship

of each of these two traits with hip height at 18 mo of age, will aid in the decision of whether or









89

not to include hip height as a selection criterion when developing breeding selection objectives

for Brahman cattle.

Hip Height and Weight at Weaning

Estimates of (co)variance components and genetic parameters for WHH and WWT are

shown in Table 5-2. The heritability estimate for WHH direct (.73) found in this Brahman herd

was somewhat larger than the estimate of .43 + .08 reported by Bourdon and Brinks (1986)

for 205-d hip height in Hereford cattle. The estimate of the maternal heritability for WHH was

.10. No comparable values for this estimate were found in the literature. The high WHH direct

heritability and a low WHH maternal heritability obtained suggest that Brahman cattle can be

selected for hip height at weaning and that genetic progress can be made by relying on direct

effects alone. However, the correlation between direct and maternal effects ( r. ) for WHH

was high and negative (-.57), suggesting that some of the same genes possess opposite effects

on direct and maternal components of WHH. This negative r4. estimate seems to indicate a

tendency for animals with superior hip height growth genes to have inferior maternal genes and

vice versa (Garrick et al., 1989; Mohiuddin, 1993). Mohiuddin (1993) suggested that this

negative correlation may be an indication that genes which partition nutrients for skeletal growth

of the young calf are partly incompatible with genes which partition nutrients for lactation. As a

consequence, if the breeding objectives in a selection program in Brahman cattle include hip

height at weaning, it should also be considered that it may lead to a reduction in maternal ability.

Under this circumstance a possible strategy would be to place emphasis on hip height maternal




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